Verify:2,578,314 x 6,321,737 = 16,299,423,011,418 ?

2,578,314 => (2+5+7+8+3+1+4)) =30 => (3+0) = 3

6,321,737 => (6+3+2+1+7+3+7)=29 => 2+9 = 11 => (1+1) = 2

3 x 2 = **6**

16,299,423,011,418 => (1+6+2+9+9+4+2+3+0+1+1+4+1+8) = 51 => (5+1) = **6**

Correct !

Hi could you explain how this works?

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Thanks for your interest.

The method above is called the Digit Sum method, here is a really nice website explaining it (http://mikespivey.wordpress.com/2011/12/27/digit-sums/)

The key theorem is that the Digit sum is actually the remainder of the number when divided by 9.

For example, for the number 82, 8+2=10, 1+0=1, and 82 divided by 9 gives remainder 1.

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