A) 11
B) 12
C) 13
D) 14
E) 15
Correct Answer: B
Solution :
Let the number of persons in the room be n, then \[^{n}{{C}_{2}}=66\] \[\Rightarrow \] \[\frac{n(n-1)}{2}=66\] \[\Rightarrow \] \[{{n}^{2}}-n-132=0\] \[\Rightarrow \] \[{{n}^{2}}-12n+11n-132=0\] \[\Rightarrow \] \[(n-12)(n+11)=0\] \[\Rightarrow \] \[n=12\] \[[\because n\ne -11]\]You need to login to perform this action.
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