I was reading about multinomial coefficient, when found this:
$\frac{N!}{k_1!\cdot k_2!\cdot k_3!}=\frac{N!}{(k_1+k_2)!\cdot k_3!}\cdot\frac{(k_1+k_2)!}{k_1!\cdot k_2!}$
Can someone show and explain me missing steps between this expressions? Thank you so much!
If I write $\frac{a}{b\cdot c} = \frac{a}{d\cdot c} \cdot \frac{d}{b}$ do you see the similarities?