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Question
Evaluate : `("n"!)/("r"!("n" - "r")!)` for n = 15, r = 8
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Solution
n = 15, r = 8
∴ `("n"!)/("r"!("n" - "r")!) = (15!)/(8!(15 - 8)!)`
= `(15 xx 14 xx 13 xx 12 xx 11 xx 10 xx 9 xx 8!)/(8! xx 7!)`
= `(15 xx 14 xx 13 xx 12 xx 11 xx 10 xx 9)/(7 xx 6 xx 5 xx 4 xx 3 xx 2 xx 1)`
= 5 × 13 × 11 × 9
= 6435
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