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Question

If Pr10=5040 . Then, find out r.


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Solution

Solution.

Prn is computed as,

Prn=n!(n-r)!

Pr10=504010!(10-r)!=5040(10-r)!=10!5040(10-r)!=10×9×8×7×6!5040(10-r)!=5040×6!5040(10-r)!=6!10-r=6r=10-6r=4

Hence, the value of r is 4.


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