Evaluate

Answer : Given, ⁿCr–1 = 36,

ⁿCr = 84 and ⁿCr+1 = 126

To find:r=?

⇒2(n-r)=3(r+1)

⇒2n-5r=3….(2)

From equations 1 & 2 we get n=9 & r=3

Ans: r = 3