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If $^{n} P_{r} = 2520 {and}^{n} C_{r} = 21$ then $n$ is is equal to:

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Correct option is B

(r!) nCr=nPr⇒(r!)(21)=2520⇒ r!=120⇒r=5Now nC5=21=12!(7×6)=7!5!2!⇒ n=7

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If nPr=2520 and nCr=21 then n is is equal to:

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If $^{n} P_{r} = 2520 {and}^{n} C_{r} = 21$ then $n$ is is equal to: