Math
Q. When your doing a multiplication problem, for example 84 times 37 = 3,108, how do you check the answer without a calculator?

A. I'm kinda confused on how to check the answer, do i do 84 times 400??
asked by
Gigi

here is a very old trick:
add up the digits of each factor
87> 8+4 = 12 , do it again  1+2 = 3
37 > 3+7 = 10 > 1+0=1
multiply them : 3*1 = 3
take the answer and add up the digits
3108 > 3+1+0+8 = 12  1+2 = 3
same result!, extremely high probability that our answer is correct
This is called "casting out nines"posted by Reiny
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