MCQ
If $^{56}{P_{r + 6}}{:^{54}}{P_{r + 3}} = 30800:1$, then $r = $
  • A
    $31$
  • $41$
  • C
    $51$
  • D
    None of these

Answer

Correct option: B.
$41$
b
(b) $\frac{{56\;!}}{{(50 - r)\;!}} \times \frac{{(51 - r)\;!}}{{54\;!}}$

$ = \frac{{30800}}{1} \Rightarrow 56 \times 55 \times (51 - r) = 30800$

$ \Rightarrow $ $r = 41$.

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