Video: Estimating Products of Two-Digit by One-Digit Numbers and Using Estimates to Check Reasonableness

We can estimate to check our work. Estimate 83 × 4 by rounding 83 to the nearest ten. Find the product. Check that your answer is reasonable using your estimate.

02:20

Video Transcript

We can estimate to check our work. Estimate 83 times four by rounding 83 to the nearest ten. Find the product and check that your answer is reasonable using your estimate.

We’ll start at the beginning. The first step tells us to estimate 83 times four by rounding 83 to the nearest ten. What is 83 rounded to the nearest ten? Three is less than five. And that means we round down. 83 rounded to the nearest ten is 80. For our estimate, we need to multiply 80 times four. Eight times four equals 32. And then we bring our zero over. 80 times four equals 320. So here’s our estimate. 83 times four is about 320.

In our next step, we want to find the product. We actually want to multiply 83 by four. We line them up vertically and then start in the ones place. Four times three equals 12. Write down your two. Carry your one. Moving on to the tens place, four times eight equals 32, plus the one we carried over equals 33. The product of 83 and four is 332.

In our last step, we check that our answer is reasonable using our estimate. If we estimated that our answer would be around 320, is 332 a reasonable answer? Yes, it is. We have an estimate of 320 and an exact answer of 332.

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