If ^n P_r = 840, ,^n C_r = 35, then n is equal to - Vidyadip

MCQ

If $^n{P_r} = 840,{\,^n}{C_r} = 35,$ then $n$ is equal to

A
$1$
B
$3$
C
$5$
✓
$7$

✓

Answer

Correct option: D.

$7$

d
(d) $\frac{{^n{P_r}}}{{^n{C_r}}} = 24 \Rightarrow r\;! = 24 \Rightarrow r = 4$

$\therefore $$^n{C_4} = 35 \Rightarrow n = 7$.

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