Question

Patrycia’s overall grade in her physics class is based solely on the average of her scores on 6 unit tests. The grade she received on the first 5 tests are as follows: 89, 93, 95, 92, 90. What grade does Patrycia need to earn on her 6th unit test to end up with a 90% in the class?

A.
76.5%
B.
81%
C.
90%
D.
92.5%

Answer 1

It would be B. 81%

I tested out each answer by finding the average:
89 + 93 + 95 + 92 + 90 + 81 = 540
540 / 6 = 90

Answer 2

(89 + 93 + 95 + 92 + 90 + x)/6 = 90%
(459 + x)/6 = 90% (multiply by 6)
459 + x = 540
x = 540 - 459
x = 81

check...
(459 + 81)/6 = 90%
540/6 = 90%
90% = 90% (correct)

She would need to have an 81