PRODUCT OF TWO
2-DIGIT NUMBERS.
The simplest case is when two numbers are not too far apart
and their difference is even, for example, let one be 24 and the other 28. Find
their average: (24 + 28)/2 = 26 and half the difference (28 -
24)/2 = 2. Subtract the squares:
28×24 = 26² - 2² = 676 - 4 = 672.
The ancient Babylonian used a similar approach. They
calculated the sum and the difference of the two numbers, subtracted their
squares and divided the result by four. For example,
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33×32
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= (65² - 1²)/4
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= (4225 - 1)/4
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= 4224/4
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= 1056.
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