Question

If ¹¹ C _r = ¹¹ C _{r – 9} , find ¹²C _r
1. 45
2. 67
3. 66
4. 25
5. 75

Answer 1

Correct Answer - Option 3 : 66

Given

¹¹ C _r = ¹¹ C _{r – 9}

Concept

If ⁿCx = ⁿC y

 ⇒ x + y = n

Calculation

⇒ r + r – 9 = 11

⇒ 2r = 20

⇒ r = 10

So, 12!/(10! × 2!)

⇒ ((12 × 11 × 10!)/(10! × 2!)

⇒ 66