NDA2019MathematicsPermutation and CombinationActual
If C (20, n +2)= C (20, n -2) , then what is n equal to?
Options
- A8
- B10
- C12
- D16
Correct answer
B. 10
Step-by-step solution
Given, C(20, n +2)= C (20, n -2) aligned & ²⁰ C _ n +2 = ²⁰ C _ n -2 & 20= n +2+ n -2 ( ^n c_r= ^n c_s n=r+s ) & 20=2 n & n =10 aligned