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 \(m=\)
  1. \(r\)
  2. \(r-1\)
  3. \(r+1\)
  4. \(1-r\)

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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