The value of $y$ varies inversely as $\sqrt x$ and when $x=24$, $y=15$. What is $x$ when $y=3$?

y = k/ (sqrtx)       k = proportionality constant

 

15 = k/sqrt(24)

15 sqrt24  = k

 

Now when y = 3

3 = 15 sqrt(24)/x

 

x = 15 sqrt (24)  / 3  = 5 sqrt 24 = 10 sqrt 6