Benchmark Percents

Finn reads this

Four percents are worth knowing cold, because you can build almost any other percent from them.

The four benchmarks

Finn reads this

1. 50 percent is half. 50% of 80 is 40.
2. 25 percent is a fourth. 25% of 80 is 20: half of half.
3. 10 percent is a tenth. Move the decimal point one place left. 10% of 80 is 8.
4. 1 percent is a hundredth. Move the decimal point two places left. 1% of 80 is 0.8.

ElleMath-speak

A benchmark percent is a common percent used for estimating.

FinnPlain English

These are the ones you can find fast. Find 10 percent first and you can build almost anything.

Build from 10 percent

Finn reads this

Want 30 percent of 80? 10 percent is 8, so 30 percent is three of those: 24. Want 5 percent? Half of 10 percent: 4. Want 15 percent? 10 percent plus 5 percent: 8 + 4 = 12. Want 35 percent? 30 percent plus 5 percent: 24 + 4 = 28.

Use the benchmarks to estimate, too. 48 percent of 200 is close to 50 percent of 200, which is 100. So the answer is a little under 100. (It is 96.)

Back to Unit 1

Elle reads this

A unit rate is how much for one. A percent is how much for 100. So a percent is a unit rate for 100 instead of for 1, and every percent problem is a proportional relationship: it always multiplies by the same number. 30 percent of anything is that thing times 0.30.

ElleMath-speak

A percent is a rate per 100, so it is a unit rate with 100 as the unit.

FinnPlain English

A percent is a unit rate for 100 instead of for 1. Same idea as Unit 1, new number.

Let me try a few

NC standards: NC.7.RP.3.

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