Fast Math Trick - Multiply a number by 999

Описание к видео Fast Math Trick - Multiply a number by 999

Multiplying a 3 digits number by 999 is similar to multiplying a two digits number by 99. In this video, I am going to show you the trick to multiply a three digits or two digits number by 999.

For example, 456 x 999. There are two steps in this trick. Step 1, reduce 456 by 1. The result is 455, and make this the first 3 digits of the asnwer. Step 2, find the 1000's complement of 456. 1000 - 456 = 544. Make this the last 3 digits of the answer.

Therefore, 456 x 999 = 455544.

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