Question

Estimate the sum of 21+17.

Answer 1

When estimating sums, you need to round to get to the answer.

So in the problem:

21+17 = ?

I round 21 to 20.

I round 17 to 20.

So know, the problem is:

20+20

The answer to 20 + 20 equals 40.

The answer is 40.

Answer 2

40 Is The Sum Of 21+17.