What this lesson shows
4.87 + 3.12 is about 5 + 3, or 8, so 7.99 is reasonable and 79.9 is not. 9.21 − 3.9 is about 9 − 4, or 5, so 5.31 makes sense. 18.6 ÷ 3 is about 18 ÷ 3, or 6, so 6.2 makes sense and 62 or 0.62 does not.
The worked example
The lesson works this one step by step: 4.87 + 3.12. Then your kid tries one like it on paper.
The steps
- Round to friendly numbers
- Work out the estimate
- Is the answer close to it?
Helping at home
Before working each problem, round to friendly numbers: whole numbers to add or subtract, a number the divisor goes into evenly to divide. Then work it out. An answer far from the estimate usually means a slipped decimal point.
If your kid gets stuck
Estimate with friendly numbers first.
Watch it with Lux
With Lux, this lesson is a narrated video and a printed page your kid works on. Then Lux helps with the same math on their own worksheet, one question at a time.