WBJEE · Maths · Binomial Theorem
If \({ }^{n} C_{r-1}=36,{ }^{n} C_{r}=84\) and \({ }^{n} C_{r+1}=126\) then the value of \({ }^{n} C_{8}\) is
- A 10
- B 7
- C 9
- D 8
Answer & Solution
Correct Answer
(C) 9
Step-by-step Solution
Detailed explanation
Given, \[ \begin{aligned} { }^{n} C_{r-1} &=36 \\ { }^{n} C_{r} &=84 \\ { }^{n} C_{r+1} &=126 \end{aligned} \] On dividing \[ \frac{r}{n-r+1}=\frac{36}{84} \] \(\Rightarrow \quad 84 r=36 n-36 r+36\) \(\Rightarrow \quad 120 r=36 n+36\) Also,…
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