Multiplying by 9 or 9’s

Any number can be multiplied by 9 by applying the following rule.

“By one less than the one before” is used here in combination with “Subtract All from 9 and Last From 10″.

763 x 999 = 762237

• 763 is first reduced by 1 (one less than the one before)

763 less 1 is 762. This is the first part of the answer.

• Then apply the rule “subtract all from 9 and the last from 10″ to 763

i.e. 7 and 6 of 763 are subtracted from 9 and last digit 3 of 763 is subtracted from 10.

(9 - 7 = 2 9 - 6 = 3 10 - 3 = 7) we get 237, which is the second part of the answer.

1867 x 99999 = 186698133

Here, as 1867 has 4 digits, and 99999 has 5 digits,

We put a zero in front of 1867 that is 01867.

• This is reduced by 1 (rule - one less than the one before) to get 1866 as the first part of the answer.

Then applying the rule - subtract all from 9 and last from 10 to get 01867 (9 - 0 = 9, 9 - 1 = 8, 9 - 8 = 1, 9 - 6 = 3, 10 – 7 = 3)

We get 98133 as the second part of the answer.

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