Multiplying Special 2-digit Numbers

42 x 48 = ?

Notice that their tens digits are the same, 4. And their ones digits sums up to 10, that is, 2 plus 8 equals 10. For special numbers like these, there is a shortcut to get the product.

To get the answer, first multiply the tens digit by itself plus 1, that is 4 x (4+1) or simply put 4 x 5.
4 x 5 = 20
20 will be the first digits of the answer. To get the remaining two digits, multiply  the ones digits 2 and 8.
2 x 8 = 16
So we have 20 and 16, put them together, we have 2016 as the answer.
42 x 48 = 2016

More examples:


53 x 57 = ?
53 x 57 = 5x6   3x7

53 x 57 = 3021

61 x 69 = ?
61 x 69 = 6x7   1x9

61 x 69 = 4209

26 x 24 = ?
26 x 24 = 2x3   6x4

26 x 24 = 624

35 x 35 = ?
35 x 35 = 3x4   5x5

35 x 35 = 1225

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