Mental Math with Tricks & Shortcuts: Multiplying by 9, 99, 999, 9999 and so on

Mental Math with Tricks & Shortcuts: Multiplying by 9, 99, 999, 9999 and so on: Tricks multiplying by 9, 99, 999, 99999 and so on provided that the number to be multiplied with be the same number digit as 9 numbered d...