Lesson 3: Estimate the Percent of a Number6.AT.4

I can…

I can estimate the percent of a number using benchmark percents, rounding, and compatible numbers.

Key words

• estimate — A reasoned answer that is close enough to be useful, found without exact computation.
• benchmark percent — A friendly percent — 1%, 10%, 25%, 50%, 75%, 100% — used as a landmark for estimating.
• compatible numbers — Numbers close to the originals that are easy to compute with mentally.
• double number line — Two parallel number lines that pair amounts with their percents at the same positions.
• the whole — The quantity that counts as 100% in a problem — and it can change between questions.

Steps

1. The whole is 6 GB — that is 100%.
2. I mark the bottom line in benchmark jumps of 25%: 0%, 25%, 50%, 75%, 100%.
3. Equivalent ratios give the top line: 25% of 6 GB is 1.5 GB, so the top reads 0, 1.5, 3, 4.5, 6.
4. 4 GB used lands between 4.5 (75%) and 3 (50%), close to 4.5 — so about 70% of the storage is used.

Try it

Estimate 19% of 412 using benchmarks or compatible numbers.

Check your answer

About 80

19% is about 20%, and 412 is about 400. 20% of 400 is 0.2 × 400 = 80.

Sentence starter

I know ___ because ___.

Goal: I can explain an estimate using the words about, benchmark, and compatible numbers.