If ^nP_r=30240 and ^nC_r=252 the the ordered pair (n,r) is equal to
(a)(12,6)
(b)(10,5)
(c)(9,4)
(d)(16,7)
(a)(12,6)
(b)(10,5)
(c)(9,4)
(d)(16,7)
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Rahul@gurome wrote:Solution:
nPr is n!/(n-r)! and nCr is n!/{r!*(n-r)!}.
So nPr/nCr is r! which is 30240/252 = 120 = 5!
So r is 5.
We need not look for n because in all options there is only one choice where r is 5.
Correct answer is (10,5).
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