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:
⇒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