Answer
$y_1=\frac{y}{10}.$
$y$ decreases $10$ times.
Work Step by Step
If $y$ varies inversely as the square root of $x$ we can write down this as
$$y=\dfrac{c}{\sqrt x},$$
where $c=const.$
So If $x_1=100x$ then
$$y_1=\frac{c}{\sqrt x_1}=\frac{c}{\sqrt{100x}}=\frac{c}{10\sqrt{x}}=\frac{y}{10}.$$
It means $y$ decreases $10$ times.
