Question

Sandra's scores on the first 4 tests were 87, 92, 76 and 89. What is the minimum score she needs to make on the fifth test so that her average is at least an 80.

Answer 1

Let the score on fifth test be x

Mean test score = (87 + 92 + 76 + 89 + x)/5

Then (87 + 92 + 76 + 89 + x)/5 >= 85

(344 + x)/5 > = 85

Multiply by 5 on each side, we will get

344 + x >= 85*5

344 + x>=425

x>= 425 - 344

x>=81