Question 36
Permutations and CombinationsSimplify: nCr ÷ nCr−1
- A.n(n − r)/r
- B.n/(r(n − r))
- C.1/(r(n − r))
- D.(n − r + 1)/r
Show the answer and explanation
Answer: D ((n − r + 1)/r)
Explanation
ⁿCᵣ/ⁿCᵣ₋₁ = [(r − 1)!(n − r + 1)!]/[r!(n − r)!] = (n − r + 1)/r.