Multiplying by 9, or 99, or 999

Multiplying by 9 is really multiplying by 10-1.

So, 9x9 is just 9x(10-1) which is 9x10-9 which is 90-9 or 81.

          Lets take an example: 38x9 = 38x(10-1) = 380-38 = 342.
  
          Lets take another example: 95x9 = 95x(10-1) = 950-95 = 855.

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

            
           So, 66x99 = 66x(100-1) = 6600-66 = 6534.


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


           38x999 = 38x(1000-1) = 38000-38 = 37962.

Posted in: Maths, Multiplication