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
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
$14$
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- [JEE MAIN 2017]
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$^n{P_r}{ \div ^n}{C_r}$ =
$^n{P_r}{ \div ^n}{C_r}$ =