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(*) Double and Half Method:

   A.  The double and half method is used to make two numbers easier to multiply.  The idea is you can double one number and half the other before multiplying.

Ex [1]  35 x 24 =_________.

a)      35 x 2 = 70.

b)      24 ÷ 2 = 12.

c)      70 x 12 = 840.

d)      The answer is 840.

Ex [2]  57 x 22 =_________.

a)      57 x 2 = 114.

b)      22 ÷ 2 = 11.

c)      114 x 11 = 1254.  See Multiplying by 11.

d)      The answer is 1254.

   B.  This method can also be adapted to multiplying and dividing the numbers by an integer other than 2.

Ex [1]  6 ¹/₄ x 96 =_________.

a)      In this example you can multiply and divide by 4.

b)      6 ¹/₄ x 4 = 25.

c)      96 ÷ 4 = 24.

d)      25 x 24 = 600.  See Multiplying by 25..

e)      The answer is 600.

Ex [2]  66 x 21 =_________.

a)      In this example you can multiply and divide by 6.

b)      66 ÷ 6 = 11.

c)      21 x 6 = 126.

d)      126 x 11 = 1386.  See Multiplying by 11..

e)      The answer is 1386.

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