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1.10: Percent Increase and Decrease

  • Page ID
    45769
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    Learning Outcome

    • Solve problems involving percent increase and decrease

    People in the media often talk about how much an amount has increased or decreased over a certain period of time — referring to politics, economics, demographics, etc. These statistical increases or decreases are usually expressed as a percent. In business, data is also often presented as percent change — analyzing profits, website traffic, customer satisfaction scores, etc.

    Percent change refers to either percent increase or percent decrease depending on how the number has gained or lost value or magnitude.

    Percent Increase

    To find the percent increase, first we find the amount of increase, which is the difference between the new amount and the original amount. Then we find what percent the amount of increase is of the original amount.

    Find Percent Increase

    Step 1. Find the amount of increase.

    • increase = new amount − original amount

    Step 2. Find the percent increase as a percent of the original amount.

    example

    In 2011, the California governor proposed raising community college fees from \text{\$26} per unit to \text{\$36} per unit. Find the percent increase. (Round to the nearest tenth of a percent.)

    Solution

    What are you asked to find? the percent increase
    Choose a variable to represent it. Let p= percent.
    Find the amount of increase. .
    Find the percent increase. The increase is what percent of the original amount?
    Translate to an equation. .
    Divide both sides by 26. {\Large\frac{10}{26}}={\Large\frac{26p}{26}}
    Round to the nearest thousandth. 0.384=p
    Convert to percent form. \text{38.4%}=p
    Write a complete sentence. The new fees represent a 38.4\text{%} increase over the old fees.

    try it

    [ohm_question]146704[/ohm_question]

    [ohm_question]146705[/ohm_question]

    Percent Decrease

    Finding the percent decrease is very similar to finding the percent increase, but now the amount of decrease is the difference between the original amount and the final amount. Then we find what percent the amount of decrease is of the original amount.

    Find percent decrease

    Step 1. Find the amount of decrease.

    • decrease = original amount − new amount

    Step 2. Find the percent decrease as a percent of the original amount.

    example

    The average price of a gallon of gas in one city in June 2014 was \text{\$3.71}. The average price in that city in July was \text{\$3.64}. Find the percent decrease.
    [reveal-answer q=”516647″]Show Answer[/reveal-answer]
    [hidden-answer a=”516647″]

    Solution

    What are you asked to find? the percent decrease
    Choose a variable to represent it. Let p= percent.
    Find the amount of decrease. .
    Find the percent of decrease. The decrease is what percent of the original amount?
    Translate to an equation. .
    Divide both sides by 3.71. {\Large\frac{0.07}{3.71}}={\Large\frac{3.71p}{3.71}}
    Round to the nearest thousandth. 0.019=p
    Convert to percent form. \text{1.9%}=p
    Write a complete sentence. The price of gas decreased 1.9\text{%}.

    [/hidden-answer]

    try it

    [ohm_question]146706[/ohm_question]

    [ohm_question]146707[/ohm_question]

    Percent Change

    In the following video we show more examples of how to find percent increase and decrease.

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    A YouTube element has been excluded from this version of the text. You can view it online here: http://pb.libretexts.org/afm-2/?p=80

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