When multiplying 2 numbers with difference of two (for example 7 and 9, 11 and 13, 24 and 26), find the square of the mean of the 2 numbers, and then subtract it by 1.
Example:
7 x 9 = 8² – 1 = 64 – 1 = 63
11 x 13 = 12² - 1 = 144 – 1 = 143
24 x 26 = 25² - 1 = 625 – 1 = 624
Exercise:
- 14 x 16 =
- 20 x 22 =
- 34 x 36 =
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