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