$\frac{a}{a+3}\ \cdot\frac{a-3}{a}\ =$

$\frac{\left(a-1\right)^2}{b-1}\ \cdot\frac{\left(b-1\right)^2}{a-1}\ =$

$x\ :\ \frac{x}{y\ }\ =$

$\frac{x\ +y}{x}\ :\ \frac{x+y}{y}=$