A student has taken n tests, and has a 90% average. What score must the student get on the next test to raise the average to 91%?
Current total: t = n*90
next score = s
New average av = (t + s)/(n + 1)
So: 91 = (n*90 + s)/(n + 1)
Rearrange to find s. You will need to know n if you want an actual number for s.
