This is a Self-Learning Module (SLM) for General Mathematics in Senior High School: Quarter 1, Module 16, “Representing Real-life Situations Using Exponential Functions.” It was developed by DepEd Region IV-A CALABARZON (First Edition, 2021) for learners studying at home or in class. After working through it, learners should be able to turn situations such as bacterial growth, radioactive decay, and bank interest into exponential models and use those models to solve problems.
What learners will learn
After going through this module, learners are expected to:
- Define exponential functions.
- Show illustrations of exponential functions that represent real-life situations.
- Represent real-life situations using exponential functions.
- Solve problems involving real-life situations using exponential functions.
What the module covers
The module has one lesson, “Representing Real-Life Situations Using Exponential Functions.” It covers population growth, exponential decay (half-life), compound interest, and the natural exponential function. It explains that exponential functions are transcendental functions because they cannot be expressed by a finite number of algebraic operations.
Key ideas and formulas
An exponential function with base b has the form f(x) = b^x (or y = b^x), where b > 0 and b ≠ 1. Examples are f(x) = 2^x, f(x) = 3^x, and f(x) = 4^x. In the review, if f(x) = 4^x, then f(2) = 16, f(−2) = 1/16, and f(1/2) = 2.
| Situation | Formula | What the letters mean |
|---|---|---|
| Growth (quantity doubles every T units of time) | y = y₀(2)^(t/T) | y₀ = initial amount, t = time passed |
| Exponential decay (half-life) | y = y₀(1/2)^(t/T) | T = half-life, the time for half the substance to decay |
| Compound interest, compounded annually | A = P(1 + r)^t | P = principal, r = annual rate, t = years |
| Natural exponential function | f(x) = e^x | e ≈ 2.71828 |
Worked examples in the module
- Bacteria growth: A culture of 300 bacteria doubles every 10 hours. The model is y = 300(2)^(t/10). After 90 hours there are 300(2)^9 = 153,600 bacteria.
- Radioactive decay: A substance loses half of itself every 5 days, starting at 50 grams. The model is y = 50(1/2)^(t/5). After 30 days, 50(1/2)^6 = 0.78125 g remain.
- Compound interest: Aling Dionisia deposits ₱10,000.00 at 3% compound interest per year. The model is A = 10,000(1.03)^t. After 11 years with no withdrawal she has ₱13,842.34. The module first adds the interest year by year (₱10,300.00, ₱10,609.00, ₱10,927.27) to show why the formula works.
- Natural exponential function: A city’s predicted population is P = 200,000e^(0.03y), where y is the number of years after 2020. For 2030, y = 10, so the predicted population is about 269,971.
The opening activity: Helping Hands
In “What’s New,” a teacher, Ms. Reyes, teaches a shortcut to one student. Each student who learns it then teaches two classmates. Learners fill in a table of tutorial stages, find the pattern f(x) = 2^x, and work out that the project reaches 512 students at stage 9. They also draw a tree diagram and reflect on the values of helpfulness and sharing.
Activities and assessments
- What I Know: a 15-item multiple-choice pretest.
- What’s More: Activity 1.1 (tables and models for bacteria, half-life, and a bank deposit) and Activity 1.2 (three word problems, including a population model with e).
- What I Have Learned: fill-in-the-blank items on the key terms and formulas, writing the steps for modeling a situation in your own words, and a reflection on how you would address population-related economic problems if you were president.
- What I Can Do: “Wise Decision and Friendship Goal,” a performance task. Learners compare two birthday gift options: a fixed ₱3,000.00 each year, or ₱400.00 doubling each year from age 19 to 25. They write equations, show the amounts in a table, and give a conclusion. It is scored with a rubric worth up to 20 points, plus up to 5 points for the conclusion.
- Assessment: a 15-item multiple-choice post-test.
- Additional Activities: study exponential models of the coronavirus.
How to use this module
- Learners: Answer the pretest first to see what you already know. Then work through the parts in order: What’s In, What’s New, What is It, What’s More, What I Have Learned, and What I Can Do. Finish with the Assessment. Write your answers on a separate sheet of paper, not on the module. Check your work honestly with the answer key at the back.
- Parents and facilitators: The module includes notes and reminders for supporting home-based learning. Help your child keep to the order of the parts, and remind them to show their solutions.
- Teachers: Use the rubric in What I Can Do to rate the performance task. Some printed answers in the key do not match the activity numbers. The What’s More answers use different starting values from the activities. For Assessment item 12, the module’s own decay formula gives 2.5 g, not the printed answer. Review these answers before you hand out the key.
Frequently asked questions
What grade and quarter is this General Mathematics module for?
It is a Senior High School General Mathematics module for Quarter 1, Module 16. Its topic is representing real-life situations using exponential functions.
What is an exponential function?
An exponential function with base b is a function of the form f(x) = b^x, where b is greater than 0 and not equal to 1. Examples are f(x) = 2^x and f(x) = 3^x.
What real-life situations does the module model with exponential functions?
The module models population and bacterial growth, radioactive decay and half-life, and compound interest on bank deposits. It also includes population predictions using the natural exponential function with base e.
Does the module have an answer key?
Yes. The back of the module has answers for the pretest (What I Know), What’s More, and the Assessment. A few printed answers do not match the activity numbers, so check them with your teacher.
What is the formula for compound interest in this module?
If a principal P is invested at an annual rate r, compounded annually, the amount after t years is A = P(1 + r)^t.
Full text of the module
The text below is a transcription of the PDF above, as printed.
General Mathematics Quarter 1 – Module 16: Representing Real-life Situations Using Exponential Functions
Senior High School
[illustration: students and a teacher studying outdoors and at a table, with a globe and a child reading by a lamp]
General Mathematics Alternative Delivery Mode Quarter 1 – Module 16: Representing Real-life Situations Using Exponential Functions First Edition, 2021
Republic Act 8293, section 176 states that: No copyright shall subsist in any work of the Government of the Philippines. However, prior approval of the government agency or office wherein the work is created shall be necessary for exploitation of such work for profit. Such agency or office may, among other things, impose as a condition the payment of royalties.
Borrowed materials (i.e., songs, stories, poems, pictures, photos, brand names, trademarks, etc.) included in this module are owned by their respective copyright holders. Every effort has been exerted to locate and seek permission to use these materials from their respective copyright owners. The publisher and authors do not represent nor claim ownership over them.
Published by the Department of Education Secretary: Leonor Magtolis Briones Undersecretary: Diosdado M. San Antonio
Printed in the Philippines by ________________________
Development Team of the Module
Writer: Dennis E. Ibarrola
Editors: Elizabeth D. Lalunio, Anicia J. Villaruel, Roy O. Natividad
Reviewers: Jerry Punongbayan, Diosmar O. Fernandez, Dexter M. Valle, Jerome A. Chavez, Mary Grace D. Constantino, Mark Angelo F. Abadilla and Moahna Aura M. Mancenido
Illustrator: Hanna Lorraine Luna
Layout Artist: Roy O. Natividad, Sayre M. Dialola and Janeth D. Bendal
Management Team: Francis Cesar B. Bringas, Job S. Zape, Jr., Ramonito Elumbaring, Reicon C. Condes, Elaine T. Balaogan, Fe M. Ong-ongowan, Hermogenes M. Panganiban, Philip B. Gallendez, Josephine T. Natividad, Anicia J. Villaruel, Dexter M. Valle
Department of Education – Region IV-A CALABARZON
Office Address: Gate 2 Karangalan Village, Barangay San Isidro, Cainta, Rizal Telefax: 02-8682-5773/8684-4914/8647-7487 E-mail Address: lrmd.calabarzon@deped.gov.ph
General Mathematics
Quarter 1 – Module 16: Representing Real-life Situations Using Exponential Functions
Senior High School
Introductory Message
This Self-Learning Module (SLM) is prepared so that you, our dear learners, can continue your studies and learn while at home. Activities, questions, directions, exercises, and discussions are carefully stated for you to understand each lesson.
Each SLM is composed of different parts. Each part shall guide you step-by-step as you discover and understand the lesson prepared for you.
Pre-tests are provided to measure your prior knowledge on lessons in each SLM. This will tell you if you need to proceed on completing this module or if you need to ask your facilitator or your teacher’s assistance for better understanding of the lesson. At the end of each module, you need to answer the post-test to self-check your learning. Answer keys are provided for each activity and test. We trust that you will be honest in using these.
In addition to the material in the main text, Notes to the Teacher are also provided to our facilitators and parents for strategies and reminders on how they can best help you on your home-based learning.
Please use this module with care. Do not put unnecessary marks on any part of this SLM. Use a separate sheet of paper in answering the exercises and tests. And read the instructions carefully before performing each task.
If you have any questions in using this SLM or any difficulty in answering the tasks in this module, do not hesitate to consult your teacher or facilitator.
Thank you.
What I Need to Know
Population growth is believed to be continuous overtime and there is an increase in growth rate over time. This scenario illustrates the exponential function. Population growth of organisms, growth of money in the bank, as well as decay of a substance, are some of the occurrences where exponential functions are used. Exponential function belongs to the so-called transcendental functions because they cannot be expressed by a finite number of algebraic operations.
In this learning module, you will familiarize more about exponential function, and how the concept of an exponential function is utilized in our daily life. This module was designed and written with you in mind. It is here to help you master representing and solving real-life situations using exponential functions.
After going through this module, you are expected to:
- Define exponential functions;
- Show illustrations of exponential functions that represent real-life situations;
- Represent real-life situations using the exponential functions; and
- Solve problems involving real-life situations using the exponential functions.
What I Know
Choose the letter of the best answer. Write the chosen letter on a separate sheet of paper.
In the exponential function f(x) = b^x, x is the ____.
a. base
b. dependent variable
c. exponent
d. independent variableWhich of the following is an exponential function?
a. f(x) = x² + 3x − 4
b. f(x) = 2^x − 3x + 4
c. f(x) = 2^(3x−4)
d. f(x) = x² + 3^x − 4Which of the given situations illustrates an exponential function?
a. The distance travelled varies directly as the speed.
b. The area of a square is s² where s is the length of the side of a square.
c. Radioactive material has a half-life of 1500 years.
d. As x increases, the value of y increases.Solve f(x) = 2^x, if x = −4.
a. 1/16
b. 1/8
c. 1/4
d. ½Which of the following depict the increase in number or size at a constantly growing rate?
a. Half-life
b. Exponential growth
c. Exponential decay
d. Compound interestWhat is the rate of change in the formula y = y₀(2)^(t/T) every T units of time?
a. doubles
b. half
c. triples
d. multiplesIn the formula A = P(1 + r)^t; what is P?
a. principal compounds
b. principal invested
c. principal time
d. principal yearWhich of the following statements modeled an exponential growth?
a. The cost of pencils as a function of the number of pencils.
b. The distance when a stone is dropped as a function of time.
c. The distance of a swinging pendulum bob from the center as a function of time.
d. The compound interest of the principal amount as a function of time.
For nos. 9-10. Suppose a culture of 300 bacteria is put in a petri dish and the culture doubles every hour.
What is the exponential model on the given situation?
a. y = 2(300)^(1/t)
b. y = 300(2)^(1/t)
c. y = 2(300)^t
d. y = 300(2)^tHow many bacteria will be there after 9 hours?
a. 93,660
b. 153,600
c. 653,100
d. 393,660
For nos. 11-12. The half-life of a substance is 400 years. Initially there are 200 grams.
What is the exponential model for the given situation?
a. y = 200(1/2)^(t/400)
b. y = 400(1/2)^(t/200)
c. y = 200(1/2)^(400/t)
d. y = 400(1/2)^(200/t)How much will remain after 800 years?
a. 100 g
b. 25 g
c. 50 g
d. 12.5g
For nos. 13-14. Lino invested ₱5,000.00 into an account which increases annually at the rate of 5.5%.
What equation best describes this investment after t years?
a. A = 5000(0.055)^t
b. A = 5000(1.055)^t
c. A = 5000(1.55)^t
d. A = 5000AHow much is his investment after 5 years?
a. ₱6,534.80
b. ₱7,843.20
c. ₱25,204.50
d. ₱45,354.80A large slab of meat is taken from the refrigerator and placed in a pre-heated oven. The temperature T of the slab t minutes after being placed in the oven is given by T = 170 − 165e^(−0.006t). What is the temperature rounded to the nearest integer after 30 minutes?
a. 32°C
b. 42°C
c. 52°C
d. 64°C
Lesson 1: Representing Real-Life Situations Using Exponential Functions
The beauty of Mathematics can be found everywhere. Sometimes, you are not aware that in front of you are situations which can be written as a Mathematics model. Some conditions in life increase and decrease tremendously such as the growth of bacteria, interest of an investment or an amount loaned, depreciation or appreciation of the market value of a certain product, and even the decay of microorganism. These real-life situations exhibit exponential patterns.
This lesson is about modeling real-life situations using exponential functions like population growth, population decay, growth of an epidemic, interest in banks and investments.
What’s In
Before you proceed to the new lesson, study the following, and recall what you have learned from the previous lesson so that you will be ready for your next journey.
Definition
An exponential function with the base b is a function of the form f(x) = b^x or, y = b^x where (b > 0, b ≠ 1). Some examples are: f(x) = 2^x, f(x) = 3^x, and f(x) = 4^x.
The following will help you to recall, how to evaluate functions.
Example 1. If f(x) = 4^x, evaluate f(2), f(−2), f(1/2), and f(π).
Solution:
f(2) = 4² = 16 f(−2) = 4^−2 = 1/4² = 1/16 f(1/2) = 4^(1/2) = √4 = 2 f(π) = 4^π
Solution:
a. Let y = number of bacteria At t = 0, y = 300 t = 10, y = 300(2) = 600 t = 20, y = 300(2)^2 = 1200 t = 30, y = 300(2)^3 = 2400 t = 40, y = 300(2)^4 = 4800
An exponential model for this situation is y = 300(2)^(t/10)
b. If t = 90, then y = 300(2)^(90/10), y = 300(2)^9, y = 153,600. There will be 153,600 bacteria after 90 hours.
Exponential Models and Population Growth Suppose a quantity y doubles every T unit of time. If y_o is the initial amount, then the quantity after t units is given by y = y_o (2)^(t/T)
Example 2
A certain radioactive substance decays half of itself every 5 days. Initially, there are 50 grams. Determine the amount of substance left after 30 days, and give an exponential model for the amount of remaining substance.
Solution:
a. Let t = time in days At t = 0, Amount of Substance = 50g t = 5, Amount of Substance = 50 (1/2) = 25 g t = 10, Amount of Substance = 50 (1/2)^2 = 12.5 g t = 15, Amount of Substance = 50 (1/2)^3 = 6.25 g
An exponential model for this situation is y = 50 (1/2)^(t/5)
b. y = 50(1/2)^(30/5) = 50(1/2)^6 = 0.78125 g
Exponential Decay The half-life of a radioactive substance is the time it takes for half of the substance to decay. The exponential decay formula is y = y_o (1/2)^(t/T).
What’s New
Helping Hands!
Read and analyze the problem carefully to complete the table and to answer the questions that follow.
Ms. Love Reyes, a Mathematics teacher introduces a new project to teach her students the values of helpfulness and sharing through peer tutoring while learning Math. She believes that her students will be more comfortable and open when interacting with a peer. To teach a short cut technique in solving rational equations and inequalities, she demonstrates the strategy to one of her students and requires this student to do the same to two of his classmates, with a condition that each student who undergoes the peer tutorial will repeat the process until everyone in the class will be able to learn the short cut technique. Also, each student is required to submit a reflection paper of their experienced while doing the peer tutoring and learning with classmates, for her to assess if she is successful to attain her objectives.
a. Based on the situation above, complete the table below.
| Tutorial Stage | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|---|
| Number of Students who undergo the tutorial | 1 |
(Hint: In 0 stage, only one student undergoes the tutorial, he is the first student chose by Ms. Reyes, stage 1 is the stage where the first students share his learning to his classmate and continue up to stage 6)
b. What pattern can be observed from the data?
c. Write a formula to determine the number of students who are already involved with the tutorial project in a particular stage?
d. If the project will be extended to other students within the school, in what stage will it reach 512 students?
e. Illustrate the situation above using a tree diagram.
[transcriber’s note: empty box provided for the tree diagram]
f. What kind of teacher is Mrs. Reyes?
g. Given a chance, will you join the project? Why or Why not?
What is It
The problem in the previous activity is an example of real-life situations using exponential functions. Hence, exponential functions occur in various real-world situations. Exponential functions are used to model and illustrate real-life situations such as population growth, radioactive decay and carbon dating, growth of an epidemic, loan interest and investments.
In the previous activity, you need to complete the table for you to see the pattern. Have you seen the pattern? The pattern represents the exponential functions. You may observe that as the stage increases, the number of students involved also increases in the pattern which is equal to f(x) = 2^x. If you got it correctly, congratulations! You already representing the exponential function to a real-life situation and I am sure you can now answer the question, if the project will be extended to other students within the school, in what stage will it reach 512 students? So, the answer is stage 9.
Going back to the project, what can you say to Mrs. Reyes? What kind of teacher is she? Well, it’s up to you to answer the question to yourself. What I believe is that, you will be lucky if you will be a student of Mrs. Reyes because she is not only teaching Mathematics but she is also infusing good values to her students. You may now reflect on the question, if given the chance, will you join the project? Why or why not?
Exponential Function
An exponential function with the base b is a function of the form f(x) = b^x or y = b^x, where (b > 0, b ≠ 1).
Some of the most common applications in real-life of exponential functions and their transformations are population growth, exponential decay, and compound interest.
The following are examples of representing an exponential function in real-life situations.
Example 1
Suppose a culture of 300 bacteria at MJD Farm is put into a Petri dish and the culture doubles every 10 hours. Give an exponential model for the situation. How many bacteria will there be after 90 hours?
Example 2 (continued from the previous page)
Hmm
Correction: the page 13 content should begin here, replacing the stray lines above.
Solution:
a. Let y = number of bacteria At t = 0, y = 300 t = 10, y = 300(2) = 600 t = 20, y = 300(2)^2 = 1200 t = 30, y = 300(2)^3 = 2400 t = 40, y = 300(2)^4 = 4800
An exponential model for this situation is y = 300(2)^(t/10)
b. If t = 90, then y = 300(2)^(90/10), y = 300(2)^9, y = 153,600. There will be 153,600 bacteria after 90 hours.
Exponential Models and Population Growth Suppose a quantity y doubles every T unit of time. If y_o is the initial amount, then the quantity after t units is given by y = y_o (2)^(t/T)
Example 2
A certain radioactive substance decays half of itself every 5 days. Initially, there are 50 grams. Determine the amount of substance left after 30 days, and give an exponential model for the amount of remaining substance.
Solution:
a. Let t = time in days At t = 0, Amount of Substance = 50g t = 5, Amount of Substance = 50 (1/2) = 25 g t = 10, Amount of Substance = 50 (1/2)^2 = 12.5 g t = 15, Amount of Substance = 50 (1/2)^3 = 6.25 g
An exponential model for this situation is y = 50 (1/2)^(t/5)
b. y = 50(1/2)^(30/5) = 50(1/2)^6 = 0.78125 g
Exponential Decay The half-life of a radioactive substance is the time it takes for half of the substance to decay. The exponential decay formula is y = y_o (1/2)^(t/T).
Example 3
Aling Dionisia deposits ₱10,000.00 in BDO that pays 3% compound interest annually. Define an exponential model for this situation. How much money will she have after 11 years without withdrawal?
Solution: Compound Interest means the interest earned at the end of the period is added to the principal and this new amount will earn interest in the nesting period.
a. At t = 0, ₱10,000 t = 1, ₱10,000 + ₱10,000(0.03) = ₱10,300.00 t = 2, ₱10,300 + ₱10,300(0.03) = ₱10,609.00 t = 3, ₱10,609 + ₱10,609(0.03) = ₱10,927.27
From the above, the principal amount together with the interest earned as computed is as follows:
At t = 0, ₱10,000 t = 1, ₱10,000(1+0.03) = ₱10,000(1.03) = ₱10,300.00 t = 2, ₱10,000(1+0.03)^2 = ₱10,000(1.03)^2 = ₱10,609.00 t = 3, ₱10,000(1+0.03)^3 = ₱10,000(1.03)^3 = ₱10,927.27
An exponential model for this situation is A = 10,000(1.03)^t
b. A = ₱10,000(1.03)^11 = ₱13,842.34 After 11 years without withdrawal there will be ₱13,842.34 in bank.
Compound Interest If a principal P (initial amount of money) is invested at an annual rate of r; compounded annually, then the amount after t years is given by A = P(1+r)^t.
Example 4
The Natural Exponential Function
While an exponential function may have various bases, a frequently used base is the irrational number e, whose value is approximately 2.71828. Because e is a commonly used base, the natural exponential function is defined as having e as the base.
The predicted population of a certain city is given by P = 200,000 e^(0.03y) where y is the number of years after the year 2020. Predict the population for the year 2030.
Solution:
The number of years from 2020 to 2030 is 10, so y = 10. P = (200,000)(2.71828)^((0.03)(10)) P = 269,971.70 The predicted population for the year 2030 is 269,971.
The natural exponential function is the function f(x) = e^x.
What’s More
Activity 1.1
Solve the following:
- A culture of 100 bacteria in a petri dish doubles every hour.
a. Complete the table.
| t | 0 | 1 | 2 | 3 | 4 |
|---|---|---|---|---|---|
| No. of bacteria |
b. Write the exponential model for the number of bacteria inside the box.
[transcriber’s note: empty box provided for the answer]
c. How many bacteria will be there after 6 hours? Solution:
Answer: ____________
- Half-life of a radioactive substance is 12 hours and there are 100 grams initially.
a. Complete the table.
| t | 0 | 12 | 24 | 36 | 48 |
|---|---|---|---|---|---|
| Amount |
Write the exponential model for the amount of substance inside the box.
[transcriber’s note: empty box provided for the answer]
b. Determine the amount of substance left after 3 days. Solution:
Answer: ____________
- Kim deposited ₱10,000.00 in a bank that pays a 3% compound interest annually.
a. Identify the given: P = _______ r = _______
b. Write the exponential model for the amount of substance inside the box.
[transcriber’s note: empty box provided for the answer]
c. How much money will he have after 2 years? Solution:
Answer: ____________
Activity 1.2
Suppose the half-life of a certain radioactive substance is 20 days and there are 10g initially. Determine the exponential model and the amount of substance remaining after 75 days.
Solution:Danzel deposited an amount of ₱10,000.00 in a bank that pays 4% annual interest compounded annually. How much money will he have in the bank after 2 years.
Solution:The population of a certain country can be approximated by the function P(x) = 20,000,000 e^0.0251x where x is the number of years. Use this model to get the approximate number of the population after 30 years.
Solution:
What I Have Learned
![illustration: hand holding a light bulb]
A. Fill in the blanks with the correct term or phrase to complete the sentence.
- A function of the form f(x) = b^x or y = b^x, where b > 0 and b ≠ 1 is called _____________.
- Suppose a quantity y doubles every T units of time. If y_o is the initial amount, then the quantity y after t units is given by the formula __________________.
- The time it takes for half of the substance to decay is called _____________.
- The exponential decay formula is ________________.
- If a principal P is invested at an annual rate of r; compounded annually, then the amount after t years is given by the formula ________________.
B. In your own words, what are the steps to represent exponential function to real-life situation?
[transcriber’s note: the original provides about twenty ruled answer lines here, which are left blank in this transcription]
C. Our population today increases exponentially which results to some economic problems. If you will become the president of the Philippines, what programs will you suggest to solve the problems? Explain.
[transcriber’s note: the original provides about thirty ruled answer lines here, which are left blank in this transcription]
What I Can Do
![illustration: hand holding flowers]
Read and understand the situation below, then answer the questions or perform the tasks that follow.
Wise Decision and Friendship Goal
Your 18-year old, senior high school best friend, is asking for your advice as to which between the two “25th birthday gift options” posted by her parents she should choose for her 25th birthday.
Option A: Her parents will give her ₱3,000.00 each year starting from her 19th birthday until her 25th birthday.
Option B: Her parents will give her ₱400.00 on her 19th birthday, ₱800.00 on her 20th birthday, ₱1,600.00 on her next birthday, and the amount will be doubled each year until she reaches 25.
Task:
You need to prepare a computation highlighting the amount of money (y) your best friend gets each year (x) starting from her 19th birthday using options A and B in tabular form. Write equations that represent the two options with a complete set of solutions. At the end of your report, write a conclusion stating the option you will choose and explain your decision.
Written Report:
Conclusion:
[transcriber’s note: the original provides about seven ruled answer lines here, which are left blank in this transcription]
Rubrics for rating the output:
| Score | Descriptors |
|---|---|
| 20 | The situation is correctly modeled with an exponential function, appropriate mathematical concepts are fully used in the solution and the correct final answer is obtained. |
| 15 | The situation is correctly modeled with an exponential function, appropriate mathematical concepts are partially used in the solution and the correct final answer is obtained. |
| 10 | The situation is not modeled with an exponential function, other alternative mathematical concepts are used in the solution and the correct final answer is obtained. |
| 5 | The situation does not model an exponential function, a solution is presented but has an incorrect final answer. |
The additional 5 points will be determined from the conclusion or justification made.
5-States a conclusion with complete and appropriate justification based on a reasonable interpretation of the data. 4-States a conclusion with enough justification, based on a reasonable interpretation of the data. 3-States a conclusion with some justification, based on a reasonable interpretation of the data. 2-States a conclusion on a reasonable interpretation of the data. 1-The conclusion is based on an unreasonable interpretation of the data.
Assessment
![illustration: hand holding a pencil]
Multiple Choice. Choose the letter of the best answer. Write the chosen letter on a separate sheet of paper.
In the exponential function f(x) = b^x, b is called as the ___________.
a. base
b. dependent variable
c. exponent
d. independent variableWhich of the following defines an exponential function?
a. f(x) = 2x^2
b. f(x) = 2x-1
c. f(x) = 3^x
d. f(x) = x^2+1Solve f(x) = 2^(x+1), if x = 2.
a. 2
b. 4
c. 8
d. 16Which of the given situations illustrate an exponential change?
a. A store has 100 regular customers and each month 5 new customers come
b. The number of organisms in a culture doubles every 5 hours
c. The monthly wage of a laborer increases by 75 every year
d. As x increases the value of y increasesWhat do you call a quantity that decreases at a rate proportional to its current value?
a. Population growth
b. Exponential growth
c. Exponential decay
d. Compound interestWhich of the following situations describe an exponential decay?
a. The number of rabbits doubles every month.
b. The population decreases every year by 100.
c. The atmospheric pressure decreases as you go higher.
d. The amount of money increases every year.What is the approximate value of e in the equation y = e^x?
a. 3.1416
b. 31.416
c. 2.71828
d. 27.1828Half-life is the time required for a quantity to reduce to half its initial value. Which of the following represents exponential function involving half-life?
a. y = y_o(2)^(t/T)
b. y = y_o (1/2)^(t/T)
c. A = P(1+r)^t
d. y = e^x.
For nos. 9-10. What if the 200 bacteria in a certain culture doubles every 3 hours?
What is the exponential model for the given situation?
a. y = 2(200)^(t/3)
b. y = 200(2)^(t/3)
c. y = 2(200)^(3/t)
d. y = 200(2)^(3/t)How many bacteria are there after 9 hours?
a. 1600
b. 1800
c. 2000
d. 2100
For nos. 11-12. The half-life of a radioactive substance is 10 days and there are 10 grams initially.
What is the exponential model for the given situation?
a. y = (1/2)(10)^(10/t)
b. y = 10(1/2)^(t/10)
c. y = 10(1/2)^(10/t)
d. y = (1/2)(10)^(t/10)What is the amount of substance left after 20 days?
a. 5 g
b. 2.5 g
c. 0.025 g
d. 1.25 g
For nos. 13-14. Alex deposited ₱1,000.00 in a bank at Lucena City that pays 5% compound interest annually.
What equation best describes this investment after t years?
a. A = 1,000 (1.5)^t
b. A = 1,000 (1.05)^t
c. A = 1,000 (15)^t
d. A = 1,000 (1.005)^tHow much money will he have after 2 years?
a. ₱1,100.50
b. ₱1,102.50
c. ₱1,201.50
d. ₱1,220.50The predicted population of a certain city is given by P = 5,000e^(0.15y) where y is the number of years after 2020. What is the population in the year 2028?
a. 6,600
b. 16,600
c. 17,600
d. 18,000
Additional Activities
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Now that you have gained skills in representing and solving real-life situations using exponential functions, try to sharpen your skill by working on the task below:
Your task is to study the exponential function of the Corona Virus. Look for the different exponential model for the virus.
Answer Key
What I Know
- C
- C
- C
- A
- B
- A
- B
- D
- D
- B
- A
- C
- B
- A
- A
[transcriber’s note: the answer key page is printed rotated; the columns were read in their upright orientation]
What’s More
a.
b. y= 10(2)^t;
c. y= 10(2)^6; 6400 bacteria
a.
y= 5(1/2)^(t/5);
y= 5(1/2)^(72/5); 0.625g
a. P=P10,000; r= 3%
A= 10,000(1.03)^t;
A= 10,000(1.03)^t ; A= P10,609
a. P(x)= 20,000(e)^((0.0251)(30))
b. 42,467
Assessment
- A
- C
- C
- B
- C
- B
- C
- B
- D
- A
- B
- C
- B
- B
- B
References
Alday, Eward M., Batisan, Ronaldo S., and Caraan, Aleli M. General Mathematics. Makati City: Diwa Learning Systems Inc., 2016. 70-76, 120-130, 176-201.
Orines, Fernando B., Esparrago, Mirla S., and Reyes, Junior. Nestor V. Advanced Algebra: Trigonometry and Statistics. Second Edition. Quezon City: Phoenix Publishing House Inc., 2004. 249-253.
Oronce, Orlando A., and Mendoza, Marilyn O. General Mathematics. Quezon City: Rex Bookstore, Inc., 2016. 186-202
Oronce, Orlando. General Mathematics. Quezon City: Rex Bookstore, Inc., 2016. 107-151
General Mathematics Learner’s Material. First Edition. 2016. pp. 77-81
*DepED Material: General Mathematics Learner’s Material
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