Unit 4, Lesson 9
Part of a Percent
Grade 7
9.2
Activity
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Find each percentage of 60. What do you notice about your answers?
30% of 60
3% of 60
0.3% of 60
0.03% of 60
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20% of 5,000 is 1,000, and 21% of 5,000 is 1,050. Find each percentage of 5,000, and be prepared to explain your reasoning. If you get stuck, consider using the double number line diagram.
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1% of 5,000
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0.1% of 5,000
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20.1% of 5,000
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20.4% of 5,000
A double number line with 12 tick marks. The first tick mark is followed by a break and then 11 evenly spaced tick marks. For the top number line, the number 0 is on the first tick mark, 1000 on the second, and 1050 on the twelfth. For the bottom number line, the percentage 0% is on the first tick mark, 20% on the second, and 21% on the twelfth. -
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15% of 80 is 12, and 16% of 80 is 12.8. Find each percentage of 80, and explain your reasoning.
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15.1% of 80
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15.7% of 80
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Student Lesson Summary
A percentage, such as 30%, is a rate per 100. To find 30% of a quantity, we multiply it by , or 0.3.
The same method works for percentages that are not whole numbers, like 7.8% or 2.5%. In the square, 2.5% of the area is shaded.
To find 2.5% of a quantity, we multiply it by , or 0.025. For example, to calculate 2.5% interest on a bank balance of \$80, we multiply , so the interest is \$2.
We can sometimes find percentages like 2.5% mentally by using convenient whole-number percentages. For example, 25% of 80 is one fourth of 80, which is 20. Since 2.5 is one tenth of 25, we know that 2.5% of 80 is one tenth of 20, which is 2.
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