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A. Multiplying by 715 is derived from Multiplying by 143. Since 715 = 1001 x (5/7) you can divide by 7, multiply by 5, and multiply by 1001.
Ex [1] 28 x 715 =_________
a) 28 ÷ 7 = 4.
b) 4 x 5 = 20.
c) 20 x 1001 = 20020.
d) The answer is 20020.
Ex [2] 714 x 715 =_________.
a) 714 ÷ 7 = 102.
b) 102 x 5 = 510.
c) 510 x 1001 = 510510.
d) The answer is 510510.