Benchmark Values: 10% and 5%

To find 10% of any number, just move the decimal point to the left one place:

10% of 500 is 50	10% of 34.99 = 3.499	10% of 0.978 is 0.0978

Once you know 10% of a number, it is easy to find 5% of that number, because 5% is half of 10%:

10% of 300 is 30	5% of 300 is 30 ÷ 2 = 15

These quick ways of calculating 10% and 5% of a number can be useful for more complicated percentages. For example:

What is 35% of 640?

Instead of multiplying 640 by 0.35, begin by finding 10% and 5% of 640:

10% of 640 is 64	5% of 640 is 64 ÷ 2 = 32

Note that 35% of a number is the same as (3 × 10% of a number) + (5% of a number):

3 × 64 + 32 = 192 + 32 = 224

You can also use the Benchmark Values to estimate percents. For example:

Karen bought a new television, originally priced at $690. However, she had a coupon that saved her $67. For what percent discount was Karen’s coupon?

You know that 10% of 690 would be 69. Therefore, 67 is slightly less than 10% of 690.

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