If $^n{P_r} = 840,{\,^n}{C_r} = 35,$ then $n$ is equal to
If $^n{P_r} = 840,{\,^n}{C_r} = 35,$ then $n$ is equal to
- A
$1$
- B
$3$
- C
$5$
- D
$7$
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