Estimating Sums By Rounding
Date: 08/16/98 at 05:53:24 From: CHASE BOYDSTON Subject: Estimating Sums By Rounding Dear Dr. Math, For our homework, we have to estimate to find the sum or difference by rounding. An example is 698 + 249. Do you think my teacher means after you get the answer, or to round the problem off before you add it? Thanks, Chase
Date: 08/18/98 at 15:24:22 From: Doctor Margaret Subject: Re: Estimating Sums By Rounding Hi Chase, Thanks for writing to Dr. Math. One of the reasons we use rounding is to try to find something out more quickly than the regular way. For example, if you had 20 dollars to spend for school supplies and you went to the store and found the following prices: Pens 1.98 Binder 7.19 Pencils .99 Notebook 3.25 Erasers .69 Whiteout 2.79 How would you know whether you could buy everything? Would you stand there with a pencil and paper and do the addition? The best way, and the quickest, would be to round off right away, like this: Pens 2.00 Binder 7.00 Pencils 1.00 Notebook 3.00 Erasers 1.00 Whiteout 3.00 Now you can run down the dollar column in your head: 2 + 7 + 1 + 3 + 1 + 3 = 17 Seventeen dollars - approximately. So your teacher probably wants you to round off stuff before you actually do the addition or subtraction. Make sure that you round off to the place that she wants. For example, 516 rounded to the nearest ten equals 520, but rounded off to the nearest hundred equals 500. This is what you have to be careful about. I hope this answers your question. Let us know if we can help with anything else. - Doctor Margaret, The Math Forum Check out our web site! http://mathforum.org/dr.math/
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