Question

${}^n{C}_{r-1}=330,{}^n{C}_r=462,{}^n{C}_{r+1}=462\Rightarrow r=$

• A. 3
• B. 4
• C. 5
• D. 6

Answer 1

The correct option is C

5

$\frac{{}^n{C}_r}{{}^n{C}_{r-1}}=\frac{462}{330}\Rightarrow \frac{n-r+1}{r}=\frac{7}{5}$
$\frac{{}^n{C}_{r+1}}{{}^n{C}_r}=\frac{462}{462}\Rightarrow \frac{n-r}{r+1}=1$
$\Rightarrow r=5$