Question
Question: \[\frac{nC_{r}}{nC_{r - 1}} =\]...
nCr−1nCr=
A
rn−r
B
rn+r−1
C
rn−r+1
D
rn−r−1
Answer
rn−r+1
Explanation
Solution
nCr−1nCr=(r−1)!(n−r+1)!n!r!(n−r)!n! ⇒ r!(n−r)!n!×n!(r−1)!(n−r+1)!
=r(r−1)!(n−r)!(n−r+1)(r−1)!(n−r)!= r(n−r+1).