In a class in which the final course grade depends entirely on the average of four equally weighted 100-point tests, Erica has scored 94, 88, and 79 on the first three.

Question

What range of scores on the fourth test will give Erica a B for the semester (an average between and , inclusive)? Assume that all test scores have a non-negative value.

Express your answer in interval notation.

Answer 1

94+88+79+x = 4(80) = 320

x= 320 -94-88-79 = 320-261= 59 needed for the 4th test score, to get a final B grade of 80

unless the instructor rounds up and 79.5 average final grade is enough to get a B, although many instructors would call that a C

then

x =4(79.5)-261 = 318-261 = 57 is enough to get an 80 B,