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6.Permutation and Combination
easy
Everybody in a room shakes hand with everybody else. The total number of hand shakes is $66$. The total number of persons in the room is
A
$11$
B
$12$
C
$13$
D
$14$
Solution
(b) $^n{C_2} = 66 \Rightarrow n(n – 1) = 132 \Rightarrow n = 12$.
Standard 11
Mathematics