Trivial Knowledge...(2)

Whenever we multiply a number, x, with any number which is a multiple of 9, and from the resulting number, add each of the result's digit. Repeat the adding process until the number is less than 10. The final result will be 9.

Illustration
Lets say we have a number y, and we multiply it with 9. Imagine we have the result as abcdef. Now add a, b, c, d, e, and f together. If the added number is bigger than 9, repeat the adding process.

Example:
71307 x 36 = 2567052 => 27 => 9

Other samples:

27182 x 9 = 244638 => 27 => 9
805767 x 9 = 7251903 => 27 => 9
864527 x 9 = 7780743 => 36 => 9
47250 x 18 = 850500 => 18 => 9
157579 x 18 = 2836422 => 27 => 9
425475 x 18 = 7658550 => 36 => 9
267332 x 27 = 7217964 => 36 => 9
65686 x 27 = 1773522 => 27 => 9
315392 x 27 = 8515584 => 36 => 9
250814 x 36 = 9029304 => 27 => 9
221679 x 36 = 7980444 => 36 => 9
503975 x 36 = 18143100 => 18 => 9
629090 x 45 = 28309050 => 27 => 9
746640 x 45 = 33598800 => 36 => 9
369225 x 45 = 16615125 => 27 => 9
721270 x 54 = 38948580 => 45 => 9
182882 x 54 = 9875628 => 45 => 9
224231 x 54 = 12108474 => 27 => 9
678067 x 63 = 42718221 => 27 => 9
577075 x 63 = 36355725 => 36 => 9
546128 x 63 = 34406064 => 27 => 9
204783 x 72 = 14744376 => 36 => 9
999818 x 72 = 71986896 => 54 => 9
349511 x 72 = 25164792 => 36 => 9
856247 x 81 = 69356007 => 36 => 9
604376 x 81 = 48954456 => 45 => 9
231362 x 81 = 18740322 => 27 => 9
431473 x 90 = 38832570 => 36 => 9
56732 x 90 = 5105880 => 27 => 9
914537 x 90 = 82308330 => 27 => 9
826210 x 99 = 81794790 => 45 => 9
716627 x 99 = 70946073 => 36 => 9
522128 x 99 = 51690672 => 36 => 9


source : トリビアの泉