Q. For $2 \geq r \leq n,^{n} C_{r} + 2 \cdot^{n} C_{r - 1} +^{n} C_{r - 2}$ is equal to

1873 277 AMUAMU 2010Permutations and Combinations Report Error

A

$^{n + 1} C_{r - 1}$

B

$2 .^{n + 1} C_{r + 1}$

C

$2 .^{n + 2} C_{r}$

D

$^{n + 2} C_{r}$

Solution:

Correct answer is (d) $^{n + 2} C_{r}$