Number 999
An interesting feature is the number 999 appears in the multiplication of it any other three-digit number. It turns out a six-digit product. The first three digits of it is a multiplied number minus one, and the remaining three numbers - "add-on" first to 9.
For example:
572
573 x 999 = 572 427
999
One has only to look at the next line in order to understand the origin of this feature:
573 000
573 x 999 = 573 õ (1000 – 1) = -573
572 427
Knowing this feature, we can "instantly" multiply any three-digit number to the number 999:
947 x 999 = 946 053
509 x 999 = 508 491
981 x 999 = 980 019 è ò. ä.
And since the number 999 = 111 = 9 x 3 x 3 x 3 x 37, you can, again with lightning speed, write whole column six-digit numbers that are multiples of 37. Who is not familiar with the properties of the number 999, of course, do this unable. In short, you can arrange to uninitiated small sessions "instant" multiplication.