AP EAMCET · Maths · Permutation Combination
If \({ }^{10} P_r=604800\) and \({ }^{10} C_r=120\) then \(r=\)
- A \(14\)
- B \(7\)
- C \(8\)
- D \(16\)
Answer & Solution
Correct Answer
(B) \(7\)
Step-by-step Solution
Detailed explanation
We know that \(10_{\mathrm{p}_{\mathrm{r}}}=10_{\mathrm{c}_{\mathrm{r}}} \cdot \mathrm{r} !\) \(\Rightarrow 604800=120 . r ! \Rightarrow r !=5040\) \(\mathrm{r} !=7 !=\mathrm{r}=7\)
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