A) 12
B) 15
C) 16
D) 9
E) 14
Correct Answer: A
Solution :
\[\frac{n(n-3)}{2}=54\] \[\Rightarrow \] \[{{n}^{2}}-3n-108=0\] \[\Rightarrow \] \[{{n}^{2}}-12n+9n-108=0\] \[\Rightarrow \] \[n(n-12)+9(n-12)=0\] \[\Rightarrow \] \[(n-12)(n+9)=0\] \[\Rightarrow \] \[n=12\] \[(\because n\ne -9)\]You need to login to perform this action.
You will be redirected in
3 sec