A) 10
B) 12
C) 9
D) 6
Correct Answer: B
Solution :
\[^{n}{{C}_{2}}-n=54\]\[\Rightarrow \]\[\frac{n\left( n-1 \right)}{2}-n=54\] \[\Rightarrow \]\[{{n}^{2}}-3n-108=0\]\[\Rightarrow \]\[n=12\]
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