Multiplying by 9, or 99, or 999

 

·       Multiplying by 9 is really multiplying by 10-1.

        So, 9×9 is just 9x (10-1) which is 9×10-9 which is 90-9 or 81.

·      Let’s try a harder example: 46×9 = 46×10-46 = 460-46 = 414.

·      One more example: 68×9 = 680-68 = 612.

       To multiply by 99, you multiply by 100-1.

        So, 46×99 = 46x (100-1) = 4600-46 = 4554.

        Multiplying by 999 is similar to multiplying by 9 and by 99.

        38×999 = 38x(1000-1) = 38000-38 = 37962

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