Mathemagics: How to Look Like a Genius Without Really Trying by Arthur Benjamin, Michael Brant Shermer

By Arthur Benjamin, Michael Brant Shermer

Utilizing confirmed strategies, this quantity indicates tips on how to upload, subtract, multiply and divide quicker than is feasible with a calculator or pencil and paper, and is helping readers triumph over their anxiousness approximately math.

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The Addition Method To use the addition method to multiply any two 2-digit numbers, all you need to do is perform two 2-by-1 multiplication problems and add the results together. For example: X 40 2 X X 46 46 = = 46 42 (40 + 2) 1840 + 92 1932 Here you break up 42 into 40 and 2, two numbers that are easy to multiply by. Then you multiply 40 x 46, which is just 4 x 46 with a 0 tacked on the end, or 1840. Then you multiply 2 x 46 = 92. Finally, you add 1840 + 92 = 1932, as diagrammed above. Here's another way to do the same problem: X 40 6 X X 42 42 46 (40 + 6) 42 = 1680 = + 252 1932 The catch here is that multiplying 42 x 6 is harder to do than multiplying 46 x 2, as in the first problem.

661,015 days, 15,864,360 hours. How many seconds in eleven years? " Colburn used the same techniques described in this book to compute problems given to him entirely in his head. For example, he would factor large numbers into smaller numbers and then multiply: Colburn once multiplied 21,734 x 543 by factoring 543 into 181 x 3. He then multiplied 21,734 x 181 to arrive at 3,933,854, and finally multiplied that figure by 3, for a total of 11,801,562. As is often the case with lightning calculators, interest in Colburn's amazing skills diminished with time, and by the age of 20 he had returned to America and become a Methodist preacher.

Let's consider the last subtraction problem that gave us some trouble: 725 - 468 (500 - 32, To begin, you subtracted 500 instead of 468 to arrive at 225 (725 - 500 = 225). But then, having subtracted too much, you needed to figure out how much too much. Using complements gives you the 14 MATHEMAGICS answer in a flash. How far is 468 from 500? The same distance as 68 is from 100. If you take the complement of 68 the way we have shown you, you will arrive at 32. Add 32 to 225 and you will arrive at 257, your final answer.

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