If \(\frac{{ }^{n+1} C_{r+1}}{{ }^{n+1} C_r}=\frac{n-r+1}{m}\), then \(m=\)
If \(\frac{{ }^{n+1} C_{r+1}}{{ }^{n+1} C_r}=\frac{n-r+1}{m}\), then \(m=\)
- \(r\)
- \(r-1\)
- \(r+1\)
- \(1-r\)
Solution
\(\begin{aligned}
& \frac{{ }^{n+1} C_{r+1}}{{ }^{n+1} C_r}=\frac{n-r+1}{m} \\
& \Rightarrow \frac{\frac{(n+1) !}{(r+1) !(n-r) !}}{\frac{(n+1) !}{r !(n-r+1) !}}=\frac{n-r+1}{m} \\
& \Rightarrow \quad \frac{n-r+1}{r+1}=\frac{n-r+1}{m} \Rightarrow m=r+1
\end{aligned}\)
Hence, option (c) is correct.
Asked in: AP EAMCET 2020 (21 Sep Shift 1)
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