If nCr–1 = 36, nCr = 84 and nCr+1 = 126, find r.

Given, nCr–1 = 36, nCr = 84 and nCr+1 = 126


To find:r=?





3(n-r+1)=7r


3n-10r=-3….(1)





2(n-r)=3(r+1)


2n-5r=3….(2)


From equations 1 & 2 we get


n=9 & r=3


Ans:r=3


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