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Evaluate (n !)/(r !(n-r)!), when n = 5, ...

Evaluate `(n !)/(r !(n-r)!)`, when n = 5, r = 2.

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`(n !)/((n-r)!)` = `(5 !)/(2 !(5-2)!)`
=`(5 !)/(2 !(3)!)`
=10
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