If ^n P_5 = 20. ; ^n P_3 , then n = - Vidyadip

MCQ

If ${}^n{P_5} = 20.\;{}^n{P_3}$, then $n = $

A
$4$
✓
$8$
C
$6$
D
$7$

✓

Answer

Correct option: B.

$8$

b
(b) $\frac{{n\;!}}{{(n - 5)\;!}} \times \frac{{(n - 3)\;!}}{{n\;!}}=20$

$ \Rightarrow $$(n - 3)(n - 4) = 20 $

$\Rightarrow n = - 1,\;8$

But $ - 1$ is not exceptable.

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