What if you knew that 25% of a number was equal to 24? How could you find that number? After completing this Concept, you'll be able to use the percent equation to solve problems like this one.
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CK-12 Foundation: 0314S The Percent Equation (H264)
Guidance
The percent equation is often used to solve problems. It goes like this:
Rate is the ratio that the percent represents ( in the second version).
Total is often called the base unit .
Part is the amount we are comparing with the base unit.
Example A
Find 25% of $80.
Solution
We are looking for the part . The total is $80. ‘of’ means multiply. is 25%, so we can use the second form of the equation: 25% of $80 is Part, or .
, so the Part we are looking for is $20 .
Example B
Express $90 as a percentage of $160.
Solution
This time we are looking for the rate . We are given the part ($90) and the total ($160). Using the rate equation, we get . Dividing both sides by 160 tells us that the rate is 0.5625, or 56.25%.
Example C
$50 is 15% of what total sum?
Solution
This time we are looking for the total . We are given the part ($50) and the rate (15%, or 0.15). Using the rate equation, we get . Dividing both sides by 0.15, we get . So $50 is 15% of $333.33.
Watch this video for help with the Examples above.
CK-12 Foundation: The Percent Equation
Vocabulary
- A percent is simply a ratio with a base unit of 100—for example, .
- The percent equation is , or R% of Total is Part.
- The percent change equation is A positive percent change means the value increased , while a negative percent change means the value decreased .
Guided Practice
$96 is 12% of what total sum?
Solution:
This time we are looking for the total . We are given the part ($96) and the rate (12%, or 0.12). Using the rate equation, we get . Dividing both sides by 0.15, we get . So $96 is 12% of $800.
Practice
Find the following.
- 30% of 90
- 27% of 19
- 16.7% of 199
- 11.5% of 10.01
- 0.003% of 1,217.46
- 250% of 67
- 34.5% of y
- 17.02% of y
- x% of 280
- a% of 0.332
- of
Texas Instruments Resources
In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities designed to supplement the objectives for some of the lessons in this chapter. See http://www.ck12.org/flexr/chapter/9613 .