If John gets a 97 on his next math test, his average will be 90. If he gets 73, his average will be 87. How many tests has John already taken?
[m*n+97] / (n+1) =90,
[m*n+73] / (n+1) =87, solve for n, m
n = 7 Number of tests before the last one
m = 89 - His average before the 8th and last test.