1.

If nPr = 720(nCr), then r is equal to: (a) 4 (b) 5 (c) 6 (d) 7

Answer»

(c) 6

Given nPr = 720(nCr)

\(\frac{n!}{(n-r)!}\) = 720 \(\frac{n!}{r!(n-r)!}\)

1 = \(\frac{720}{r!}\)

r! = 720

r! = 6 x 5 x 4 x 3 x 2 x 1

r! = 6! 

r = 6



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