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Given that nPr=90 and nCr=15, find t...

Given that nPr=90 and nCr=15, find the value of r.

A.

2

B.

3

C.

5

D.

6

Correct answer is B

nPrnCr=n!(nr)!n!(nr)!r!=9015=6

n!(nr)!×(nr)!r!n!=r!=6

r=3