Answer :


Given: n+1Cr+1 : nCr = 11 : 6 and nCr : n–1Cr–1 = 6 : 3

To Find:n & r


We use this property in this question:



n+1Cr+1 : nCr = 11 : 6





6(n+1)=11(r+1)


6n+6=11r+11


6n-11r=5 …(1)


nCr : n–1Cr–1 = 6 : 3





n=2r…(2)


Using equations 1 & 2 we get


6(2r)-11r=5


12r-11r=5


r=5


n=2×5


n=10


Ans:n=10 & r=5


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