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