If n is an integer between 0 and 21 then the minimum value of n! and (21- n)! is attained for n equals to
Multiply and divide n!(21-n)! by 21!, you get n!(21-n)! =
so,minimum value of the given term is same as maximum of 21 C n
we know the max of is for r = n-1/2 if n is odd
therefore for n= 10 or 11 {both same value}, is maximum ,hence given term is minimum
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