How much should Kelly score on her third test to get an average of 91, if her previous scores are x+88 and 90-x ?

Answer 1

Assuming the third score is y

Average of three rest is 91

Means that the total score of three test is

3 times 91 which is 273

Total score of three test is 273

First score + second score + third score = 273

x + 88 + 90 - x + y = 273

178 + y = 273

y = 273 - 178

y = 95