Permutation problem

CPT 2870 views 2 replies

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Q nCr-1=56, nCr=28 and nCr+1=8, then r is equal to

A}8

B}6

C}5

D}none

Replies (2)

Ankit Hinduja

Student

1227 Points Joined June 2011

See Manish , divide nCr-1 and nCr ( i.e. nCr-1/nCr =56/28).. So after solving we get the foll. Eqn. 3r=2n+2 .... Ab aise hi divide nCr/nCr+1 = 28 /8 ... So we get another eqn. That is 9r= 7n-2.. Now solving these two equations we will get r=6..

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Q A comminity of 3 ladies and 4 gents is to be formed out of 8 ladies and 7 gents. Mrs X refuses to serve in a committee in which Mr Y is the member. the number of such committes is

A}1530

B}1500

C}1520

D}1540