Answer with explanation:
[tex]_{r}^{n}\textrm{P}[/tex] = Permutation of n things taken r at a time
[tex]_{r}^{n}\textrm{C}[/tex]=Combination of n things taken r at a time
[tex]_{r}^{n}\textrm{P}=\frac{n!}{(n-r)!)}\\\\_{r}^{n}\textrm{C}=\frac{n!}{r!\times(n-r)!)}[/tex]
[tex]_{r}^{n}\textrm{C}[/tex] contains one term r!, in the denominator which is not in [tex]_{r}^{n}\textrm{P}[/tex].
When we divide [tex]_{r}^{n}\textrm{P}[/tex] by r! that is [tex]\frac{_{r}^{n}\textrm{P}}{r!}=_{r}^{n}\textrm{C}[/tex]
