Question

Evaluate C7, 5). A. 21 B. 42 C. 1,008

Answer 1

Answer: A.  21

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C(n, r) = (n!)/(r!*(n-r)!) is the combination formula

C(7, 5) = (7!)/(5!*(7-5)!)

C(7, 5) = (7!)/(5!*2!)

C(7, 5) = (7*6*5!)/(5!*2!)

C(7, 5) = (7*6)/(2!) ..... note the "5!" terms divided and canceled

C(7, 5) = (7*6)/(2*1)

C(7, 5) = 42/2

C(7, 5) = 21