Exponential Growth And Decay – Formula, Definition With Examples

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    Welcome to another exciting exploration with Brighterly, where we light the path to understanding complex mathematical concepts. Today, we’re demystifying a key mathematical concept that we encounter more often in our daily lives than we realize: Exponential Growth and Decay.

    Have you ever wondered how a population of a species grows rapidly or how radioactive materials lose their potency over time? Behind these phenomena are the principles of exponential growth and decay, respectively. By learning these concepts, you can gain insight into diverse fields such as economics, biology, and physics. So, let’s dive into this fascinating world of exponential changes!

    What Are Exponential Growth and Decay?

    Exponential growth and decay are foundational mathematical concepts used to describe patterns of increase or decrease where the rate is proportional to the current value. These concepts play a pivotal role in a variety of disciplines such as physics, economics, biology, and more. It’s like watching a plant grow or seeing your savings account balance decrease – it’s all about the changes over time.

    They’re terms that might sound intimidating, but once you get the hang of them, they become as simple as adding two and two. Let’s break down these concepts into digestible chunks.

    Definition of Exponential Growth

    Exponential growth, simply put, occurs when the growth rate of a mathematical function is proportional to the function’s current value. In layman’s terms, it means that the larger something gets, the faster it grows. You can witness this phenomenon in various real-world scenarios such as compound interest, population growth, and even the spread of diseases.

    Definition of Exponential Decay

    Conversely, exponential decay happens when a quantity decreases at a rate proportional to its current value. Common examples of exponential decay include radioactive decay, depreciation of assets, and discharge of a capacitor in electronics. Like a snowball rolling down a hill, it starts fast and gradually slows down.

    Properties of Exponential Growth and Decay

    Properties of Exponential Growth

    1. The quantity under consideration grows by a fixed percent over equal intervals of time. This means that if you’re looking at a graph of exponential growth, it’ll show a curve that gets steeper and steeper.

    2. The base of the exponential function is a positive real number greater than 1.

    3. The function has a horizontal asymptote, typically the x-axis.

    Properties of Exponential Decay

    1. Exponential decay involves a quantity that decreases at a rate proportional to its current value. In other words, the larger the quantity, the faster it decays, but as the quantity gets smaller, the decay rate also slows down.

    2. The base of the exponential decay function is a positive real number less than 1.

    3. Like exponential growth, exponential decay also has a horizontal asymptote, usually the x-axis.

    Difference Between Exponential Growth and Decay

    Exponential growth and decay are two sides of the same coin, the primary difference lies in the direction of change. While exponential growth deals with the continuous increase of a quantity, exponential decay conversely involves the continuous decrease of a quantity.

    Formulas for Exponential Growth and Decay

    Writing Formulas for Exponential Growth

    The general formula for exponential growth is N(t) = N0e^(kt), where:

    • N(t) is the quantity at time t,
    • N0 is the initial quantity,
    • k is the growth rate,
    • e is Euler’s number (approximately equal to 2.71828), and
    • t is the time.

    Writing Formulas for Exponential Decay

    The general formula for exponential decay, on the other hand, is N(t) = N0e^(-kt), which is very similar to the growth formula but includes a negative sign in the exponent.

    Practice Problems on Exponential Growth and Decay

    Try solving these practice problems to sharpen your understanding of exponential growth and decay. Remember, the key to mastering any mathematical concept lies in continuous practice.

    Problem 1: A colony of bacteria doubles every hour. If there are 500 bacteria in the initial population, how many bacteria will there be after 6 hours?

    Hint: This is an exponential growth problem, so we use the formula N(t) = N0e^(kt). Here, the growth rate k is 100% or 1 (when expressed as a decimal), and the doubling time is 1 hour.

    Problem 2: A radioactive substance decays at a rate of 2% per day. How much of a 100 gram sample will be left after 30 days?

    Hint: This is an exponential decay problem. Use the formula N(t) = N0e^(-kt), where k = 0.02 (2% as a decimal) and t = 30 days.

    Problem 3: The population of a city is growing at 3% per year. If the current population is 200,000, what will be the population in 10 years?

    Hint: This is another exponential growth problem. Use the growth formula N(t) = N0e^(kt), with k = 0.03 and t = 10 years.

    Problem 4: A car depreciates at 8% per year. How much will a car, originally worth $25,000, be worth in 5 years?

    Hint: This problem involves exponential decay due to depreciation. Use the decay formula N(t) = N0e^(-kt), with k = 0.08 and t = 5 years.

    Take your time to solve these problems and don’t forget to cross-check your answers using your understanding of exponential growth and decay. If you get stuck, revisit the formulas and their definitions.


    Exponential growth and decay are all around us, from the interest in our savings account to the population of bacteria in a petri dish. Understanding these concepts opens a window to a deeper understanding of the world we live in. As we have seen, these concepts are not as daunting as they might first appear.

    At Brighterly, we aim to empower our learners with knowledge that they can apply in their daily lives. Remember, mathematics is a tool that enables us to quantify and make sense of our world. With your newly found understanding of exponential growth and decay, you’re one step further on this journey. Stay curious and keep exploring. Brighterly is here to illuminate your path.

    Frequently Asked Questions on Exponential Growth and Decay

    What is the importance of exponential growth and decay in real life?

    Exponential growth and decay play critical roles in various aspects of real life. Exponential growth can be seen in areas like population growth, compound interest in finance, and the spread of viruses in biology. Exponential decay, on the other hand, is crucial in understanding concepts such as depreciation of assets, radioactive decay in nuclear physics, and decay of learning in psychology.

    How can I tell if a graph represents exponential growth or decay?

    An exponential growth graph is a curve that becomes steeper over time, moving upwards to the right. On the other hand, an exponential decay graph also forms a curve but it goes downwards to the right, indicating a decrease.

    Are there any exceptions or limitations to the exponential growth and decay model?

    While exponential growth and decay models are powerful, they don’t apply to all situations. For instance, exponential growth cannot continue indefinitely – resources are finite, and at some point, growth must slow due to constraints. Similarly, exponential decay might not accurately depict scenarios where the decay rate changes over time.

    What are the base numbers in exponential growth and decay formulas?

    In the formulas for exponential growth and decay, the base number ‘e’ is a mathematical constant approximately equal to 2.71828. It’s known as Euler’s number, named after the Swiss mathematician Leonhard Euler.

    Remember, Brighterly is always here to help illuminate the path of knowledge for you. If you have any more questions or if something isn’t quite clear, don’t hesitate to reach out. Learning is a journey, and we’re honored to be a part of yours!

    Information Sources:
    1. Exponential Growth and Decay – Wolfram MathWorld
    2. Exponential Growth – Wikipedia
    3. Exponential Decay – Wikipedia

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