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Math tricks

11 times any two-digiter

To multiply, say, 11 x 32, add the digits of 32 (3 + 2 = 5) and insert the sum between them: 352.

Numbers with two-digit sums use a slight variation: For 11 x 84 (8 + 4 = 12), add the 1 from 12 to the 8 and leave the 2 in the middle: 924.

Square off

To square a number like 14, identify the preceding round number — in this case, 10. Since you subtracted 4 to get 10, add 4 to 14 to get 18 and multiply that by 10 (*the round number). Add to that the square of 4: 180 + 16 = 196.

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  1. December 21, 2009 at 6:17 pm

    good one…

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