When you estimate you round the numbers and then work it out in your head.
That way you quickly get an approximate result.
Example: 48 + 29
48 is almost 50, and 29 is almost 30.
So work out 50 + 30 = 80.
The right answer is close to 80.
Then choose the number that fits best.
The numbers filled in show the solution.
Sometimes you are not estimating a calculation but a size: about how long or how heavy something is, without measuring it.
Example: A banana weighs about ...
A banana fits easily in one hand, much lighter than a full water bottle.
100 g fits best - 10 g would be almost nothing, 1 kg would be as heavy as ten bananas together.
Examples
Example: Estimating
Example: Estimating sizes
For parents
What does this exercise practice?
Estimate results by rounding and judge them sensibly.
Common pitfalls
Children sometimes round in the wrong direction. Say it out loud: 38 is closer to 40 than to 30.
How to practice at home
While shopping, round the prices roughly and add them up in your head, then compare with the receipt.
Related: What does multiplying mean?, Comparing numbers