 numbers together and you would throw out the nines, so it would be 3942 (0) - 1581 (6) so what wwould the answer be? (3?) How do you get that though ?
Date: 03/24/2003 at 12:40:37 From: Doctor Peterson Subject: Re: Casting out nines Hi, Sarah. I would usually check a subtraction by checking the equivalent addition; here 2361 + 1581 = 3942. In this case, the reduced digit sums are 3, 6, and 0, which is correct since 3+6=9 which reduces to 0. But you can cast out nines to check subtraction directly, if you add one step. In this example you want to subtract 6 from 0. To make the 0 big enough to subtract, you can "borrow" a 9, by adding 9 to the zero. (Just as you reduce by casting out nines, you can grab an extra nine when you need one.) Now you are subtracting 6 from 9, which gives you the 3 you expect. If you have any further questions, feel free to write back. - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/
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