If 15Cr : 15Cr – 1 = 11 : 5, find r.
Given:
⇒
We know that
And also n! = n(n – 1)(n – 2)…………2.1
⇒ 5(16 – r) = 11r
⇒ 80 – 5r = 11r
⇒ 16r = 80
⇒ r = 5
∴ The value of r is 5.