# Video: Estimating Differences between Two-Digit Numbers

Hannah wants to estimate 42 − 17. She decides to round the numbers to the nearest ten. Pick the calculation she should do to estimate. [A] 50 − 20 [B] 40 − 10 [C] 40 − 20 [D] 50 − 10. Estimate 42 − 17.

02:15

### Video Transcript

Hannah wants to estimate 42 minus 17. She decides to round the numbers to the nearest 10. Pick the calculation she should do to estimate. Then estimate 42 minus 17.

The first part of our question asks us to pick the calculation she should use. In order to do that, we first need to round 42 to the nearest 10. To do that, we’ll look at the digit in the ones place. In this case, there’s a two. Because the two is less than five, we will round down. 42 is closest to the number 40. 42 rounded to the nearest 10 is 40. We can eliminate any answer choice that doesn’t round 42 to 40.

Now we need to round 17 to the nearest 10. To do that, we’ll look at the ones place. 17 has a seven in the ones place. And that is larger than five and tells us that we need to round 17 up to the number 20. 17 rounded to the nearest 10 is 20. Any answer choice that doesn’t round 17 to 20 is not correct.

The calculation Hanna should use to estimate is 40 minus 20. Now we can move on to the second part of the question that asks us to estimate 42 minus 17. We’ve already found that estimating should be 40 minus 20. And 40 minus 20 equals 20.