Answer
reduced to one third
Work Step by Step
Step 1. As $y$ is directly proportional to $x$, we have $y=kx$ where $k$ is a constant.
Step 2. If $x'=\frac{x}{3}$, we have $y'=k\frac{x}{3}=\frac{1}{3}y$
Step 3. Thus, $y$ will be reduced to one third of its original value.