Question Video: Estimating Decimal Sums and Differences by Rounding to the Nearest Whole Mathematics • 5th Grade

Look at how Jennifer estimates the sum of decimal numbers by rounding each number to the nearest whole number. She found that the sum of 3.6 and 4.27 is about 8. Estimate the sum by rounding each number to its nearest whole number. 7.43 + 6.51 = _. Estimate the difference by rounding each number to its nearest whole number. 12.77 − 5.29 = _.

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Video Transcript

Look at how Jennifer estimates the sum of decimal numbers by rounding each number to the nearest whole number. She found that the sum of 3.6 and 4.27 is about eight. Estimate the sum by rounding each number to its nearest whole number. 7.43 plus 6.51. Estimate the difference by rounding each number to its nearest whole number. 12.77 subtract 5.29.

First, we need to estimate the sum of 7.43 and 6.51. First, we have to round 7.43 to the nearest whole number. Seven is the whole number in 7.43. And to help us decide whether to round this number up or down, we need to look to the digit to the right, which is the tenths digit. 7.43 has four tenths. So 7.43 is less than five tenths. So we need to round it down. The nearest whole number is seven. The tenths digit in 6.51 is a five. So we need to round up to the next whole number, which is also seven. Seven plus seven is 14. We estimated the sum of 7.43 and 6.51 by rounding each number to its nearest whole number. Seven plus seven equals 14. Our estimate is 14.

For the second part of this question, we need to estimate the difference between 12.77 and 5.29. If we round 12.77 to its nearest whole number, we will have 13. We have 12 and seven tenths. Seven is more than five. So we rounded up to 13. And 5.29 has two tenths, which we would round down. The nearest whole number to 5.29 is five. Now, we can find the difference between 13 and five, which is eight. We estimated the difference by rounding each number to its nearest whole number.

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