Statistics
posted by Bob .
An instructor has graded 25 exam papers submitted by students in a class of 26 students, and the average so far is 71. (The maximum possible score is 100.)
A) To raise the class average by 1 point, the score on the last paper has to be:

71 = S/25 so S = 1775 the present sum of all scores after 25 grades
72 (26) = (1775+x)
1872 = 1775 + x
x = 97