MULTIPLICATION BY 5

 

 

  1. When multiplying by 5, it is easier to divide by 2 and multiply by 10.

  2. If the number you are multiplying is odd, then the last number will be a 5 (see Ex [2]), otherwise the last number is 0.

       Ex [1]  5 x 142 =_________.

a)      142 ÷ 2 = 71.  Write 71.

b)      Since 142 is even the last number is 0.  Write 0.

c)      The answer is 710.

       Ex [2]  5 x 142857 =_______.

a)      142857 ÷ 2 = 71428 with a remainder of 1.  Write 71428.

b)      Since there is a remainder of 1, the last number is 5.  Write 5.

c)      The answer is 714285.

Note: This trick works because 5 = 10 ÷ 2.