MCQ
If $^n{P_r}$=$ 720$.$^n{C_r},$ then $r$ is equal to
- ✓$6$
- B$5$
- C$4$
- D$7$
✓
Answer
Correct option: A.
$6$
a
(a) $^n{P_r}\, = 720.{\,^n}{C_r}$
(a) $^n{P_r}\, = 720.{\,^n}{C_r}$
==> $^n{P_r}\, \div {\,^n}{C_r}\, = 720$
==> $\,r\,! = 720 = 6\,!$
$==> r = 6.$
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