Assume that the average of a math test is $90$ points out of $100$ points. If the sum of the scores of all students who took the test is a four digit integer $a95b$,
(1) Find the values of $a$ and $b$
(2) How many students took the test?
I don't even know where to begin. I wonder if there is a way I can utilize the "average" and have the total sum scores divided by the number of students equal $90$, but the only thing I really know (other than that) is it's a four digit number $a95b$. And we don't know the number of students that took the test; so I'm stuck.