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Question
Evaluate `("n"!)/("r"!("n" - "r")!)` when n = 10, r = 3
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Solution
n = 10, r = 3
`("n"!)/("r"!("n" - "r")!) = (10!)/(3!(10 - 3)!)`
= `(10!)/(3!7!)`
=`(10 xx 9 xx 8 xx 7!)/(3 xx 2 xx 1 xx 7!)`
= `(10 xx 9 xx 8)/(3 xx 2 xx 1)`
= 10 × 3 × 4
= 120
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