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January 29, 2015

January 29, 2015

Posted by **abraham** on Friday, January 21, 2011 at 8:03am.

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**drwls**, Friday, January 21, 2011 at 8:22amI don't see how one would get an exact answer by rounding.

Try using this:

(a -c)(b +c) = ab + (a-b)c - c^2

with a = 30, b = 20 and c = 5

25 * 25 = 600 + 50 - 25 = 625

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**Jen**, Friday, January 21, 2011 at 10:55amI would round by doing 20 * 30, since 25 is exactly halfway between. 2 * 3 = 6, put 2 0's on the end..600

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**drwls**, Friday, January 21, 2011 at 11:05am"Estimating the exact product" seems like an oxymoron to me.

- math -
**555 plus 400**, Sunday, September 16, 2012 at 10:48pm955

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