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