Question

A student has earned the following scores on four 100-point tests this marking period: 63, 72, 88, and 91. What score must the student earn on the fifth and final test of the marking period to earn an average test grade of 80 for the five tests?

Answer 1

86

Explanation:

if their average was 80 then they would score `5xx80=400` points in total

63+72+88+91=314

400-314 = 86.

Another way to look at it:

63 is 17 short of 80
72 is 8 short of 80
88 is 8 more than 80
91 is 11 more than 80

so if you take the 8 from the 88 and put it with the 72 that would make both 80. Then take the 11 from 91 and put it on the 63 that would make 74 so still 6 short. Therefore the last score needs to be 80 plus 6