Posted by abraham on Friday, January 21, 2011 at 8:03am.
I 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
I would round by doing 20 * 30, since 25 is exactly halfway between. 2 * 3 = 6, put 2 0's on the end..600
"Estimating the exact product" seems like an oxymoron to me.
955
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