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NCERT Class XI Mathematics - Permutations and Combinations - Solutions

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Question : 10
Total: 41
Evaluate
n!
(n−r)!
 , when
(i) n = 6, r = 2 (ii) n = 9, r = 5.
Solution:  
(i)
6!
(6−2)!
 =
6!
4!
 =
6×5×4!
4!
 = 30
(ii)
9!
(9−5)!
 =
9!
4!
 =
9×8×7×6×5×4!
4!
 = 15120
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