text: i am taking a series of exams. i will have to score 97 on the last one to average 90 for the entire series.? but even if i score as low as 73, i will still average 87. how many exams are in the series? assume you have y tests  then according to the information y x 90 = subtotal + 97  ...1(equating total marks)  also  y x 87 = subtotal + 73  ...2  subtracting equation 2 from 1 you get  3y = 24 hence y= 8 tests  in the equations y x 90 is number of tests x average = total subtotal is the total without the marks of the last test