Idea 13of 24Builds onEstimate a decimal sum
Estimate the change
About how much change should you get back?
Today you'll discover
- how to round a price
- how to estimate a difference
- how to check the exact change
Think firstA $12.85 book, paid with a $20 bill
You pay $20.00 for a $12.85 book. About how much change will you get?
Decide first, then press Next. Round each amount to a whole dollar first.
A number line from $12 to $20 with dots at $12.85 and $20.00. A curved arrow takes $12.85 to $13, boxed under the line. Then the estimate $20 − $13 = about $7, and the exact change $7.15, close to $7. The last step shows 9.32 and 4.75 on a line from 4 to 10.
See the whole ideathe big idea and the key word, in one place
The big idea
To estimate a difference, round each number first, then subtract the whole numbers.
At the grocery storeMilk is $4.79 and bread is $2.35: about $5 + $2 = $7, so a $10 bill is plenty.
Easy to get wrongRound $12.85 to $13, not $12: 85 cents is closer to a whole dollar than to nothing.
Key word
- difference
- the answer to a subtraction: how much more one number is than another
Ready to use it?
- Estimate a difference of decimal numbers.
- Estimate the change from a purchase.