A) 1
B) 2
C) 3
D) 4
Correct Answer: B
Solution :
Using \[\frac{{{\,}^{n}}{{C}_{r}}}{^{n}{{C}_{r-1}}}=\frac{n-r+1}{r},\] \[\frac{{{\,}^{n}}{{C}_{r}}}{^{n}{{C}_{r-1}}}=\frac{45}{10}\]and \[\frac{{{\,}^{n}}{{C}_{r+1}}}{^{n}{{C}_{r}}}=\frac{120}{45}\] \[\Rightarrow \] \[\frac{n-r+1}{r}=\frac{9}{2}\] and \[\frac{n-r}{r+1}=\frac{8}{3}\] \[\Rightarrow \] \[\frac{8}{3}(r+1)+1=\frac{9}{2}r\] \[\Rightarrow \] \[16r+16+6=27r\] \[\Rightarrow \] \[11r=22\] \[\therefore \] \[r=2\]You need to login to perform this action.
You will be redirected in
3 sec