16. Two numbers $x$ and $y$ have a product which is equal to their sum. Which of these expressions gives $x$ in terms of $y$ ?
A $\frac{y}{y-1}$
B $\frac{y}{y+1}$
C $\frac{y+1}{y}$
D $\frac{y-1}{y}$
$\mathrm{E} \frac{y^{2}}{y+1}$
16. A We are given that $x y=x+y$. So $x y-x=y$. Therefore $x(y-1)=y$ and hence $x=\frac{y}{y-1}$. (Note that division by $y-1$ is allowed because if $y=1$, then we have $x=x+1$ which is impossible.)