Consider a number a. By the definition of multiplication, a multiplied by another number n can be written as n times the addition of a.
a* n =a+a+... +a_(ntimes)
If n=1, the sum has only one term.
a* 1 =a_(1time)
Therefore, a* 1 is equal to a. Also, by the Commutative Property of Multiplication, 1* a=a.
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