$\mathrm {\left\lfloor\mathbf{r} \cdot{ }^{n} \mathbf{C}_{\mathbf{r}}=?\right.}$

$\mathrm { \frac{\lfloor {n}}{\lfloor(n-r)}}$

$\mathrm { \frac{\lfloor {n}} r}$

$\mathrm { \frac{\lfloor {n}}{\lfloor {r}}}$

$\mathrm { \frac{\lfloor {(n-r)}}{\lfloor{r}}}$