BITSAT2011MathematicsPermutation and CombinationActual
If ( ²⁰ C _ r = ²⁰ C _ r -10 ) then ( ¹⁸ C _ r ) is equal to
Options
- A4896
- B816
- C1632
- DNone of these
Correct answer
B. 816
Step-by-step solution
( ²⁰ C _ r = ²⁰ C _ r -10 r +( r -10)=20 r =15 ) ( ¹⁸ C _ r = ¹⁸ C ₁₅= ¹⁸ C ₃= 18 17 16 1 2 3 =816 )