Video: Estimating the Sum of Two Three-Digit Numbers by Rounding to the Nearest Hundred

Look at how James estimated the sum. Estimate the sum of 731 + 119 by rounding both numbers first to the nearest hundred. Estimate the sum of 475 + 126 by rounding both numbers first to the nearest hundred.

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Video Transcript

Look at how James estimated the sum. Estimate 482 plus 316. First, round. 482 to 500, 316 to 300. Then, calculate. 500 plus 300 equals 800. Estimate the sum of 731 plus 119 by rounding both numbers first to the nearest 100. Estimate the sum of 475 plus 126 by rounding both numbers first to the nearest 100.

The first part of the question asks us to estimate the sum of 731 and 119. First, we have to round the numbers to the nearest 100. 731 comes between 700 and 800. 731 would be about here on the number line. It’s less than the halfway point 750. So we could round it to 700. The nearest 100 to 731 is 700. 119 is between 100 and 200. It’s less than 150. So we would round it down to 100. The nearest 100 to 119 is 100. Now that we’ve rounded both numbers to the nearest 100, we can calculate. 700 plus 100 equals 800. We estimated the sum of 731 and 119 by rounding both numbers first to the nearest 100. 700 and 100 gives us a total estimate of 800.

The second part of the question asks us to estimate the sum of 475 and 126. We need to follow the same steps as before. First we round both numbers to the nearest 100. 475 to the nearest 100 is 500. 126 to the nearest 100 is 100. Then, we calculate. 500 plus 100 is 600. We rounded 475 and 126 to the nearest 100. Then added 500 and 100 to give us our estimate of 600.

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