This is an interesting little question. :)
Zep, the answer is 30 becasue the only numbers that work are 25 and 36.
\((The\;\;number\;\; is \;\;10a+b\\ where\\ 10a+b=\frac{ab}{\frac{a}{b}}\\ 10a+b=b^2\\ 10a=b^2-b\\ 10a=b(b-1)\\ \)
Also
0
The only numbers where b(b-1) is a multiple of 10 is b=5 and b=6
You can take it from there.
I've redone some of the latex, I hope it works this time. I see Heueka has used Latex sucessfully since I last posted.