$^n{C_r}\,{ \div ^n}{C_{r - 1}} = $
$^n{C_r}\,{ \div ^n}{C_{r - 1}} = $
- A
$\frac{{n - r}}{r}$
- B
$\frac{{n + r - 1}}{r}$
- C
$\frac{{n - r + 1}}{r}$
- D
$\frac{{n - r - 1}}{r}$
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