If  n+1Cr+1:nCr:Cr−1   n−1=11:6:3, then nr =

Given, n+1Cr+1 nCr=116 or n+1r+1×nCr nCr=116or 6n+6=11r+11 or 6n−11r=5            (1)Also, nCr n−1Cr−1=63 or nr×n−1Cr−1 n−1Cr−1=63  or n=2r       (2)From (1) and (2), r = 5 and n = 10,∴ nr=50