Square any number in your head

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/the-magic-of-math-arthur-benjamin_aka mathemagician

Whatever number you have, subtract or add single digits to the closest multiple of 10 Ex: 12 subtract 2 to reach 10, anyone can do multiples of 10 in their head. Now add to the original number the same amount you subtracted, 12 + 2 = 14, 10 x 14 is 140. Now go to the number you subtracted and added, in this case 2, and square it 2x2=4, add 4 to your first sum, 144 is the square of 12 (but we all knew that anyhow) 96 squared means adding 4 to get to a 100, subtracting 4 to 92, 100 x 92 = 9200. Square the 4 that you added and subtracted.. 4 x 4 =16 96 squared is 9216

btw, you could do the 12 square by adding 8 to get to 20, subtracting 8 to get to 4,

4 x 20 =80 square the 8 for 64, 80+ 64 =144. Just get to the closest 10 multiple whether it's 20, 50, 100

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douglaslee
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Jul. 31, 2007 3:01 pm

Comments

46 squared: add 4 for 50, subtract 4 for 42, 50 x 42 = 2100*, 4x4=16, 2116 is the square of 46,

*100 times 42 is 4200, half is 2100

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douglaslee
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Jul. 31, 2007 3:01 pm

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