Question 121377: Mark wants to have a semester average of 85 in his math class. The three 6-week grades and the semester exam grade count equally in figuring the semester average in his school. The first six weeks Mark scored 92, the second six weeks he scored 75, and the third sixweeks Mark scored 83. What does Mark score on the semester exam to have exactly an 85 average for the semester?
It is a multiple choice question, but instead of going through all of the answers and wasting time, I would rather if you could explain to me how to do this problem faster[if there is one].
Answer by checkley71(8403)   (Show Source):
You can put this solution on YOUR website! (92+75+83+x)/4=85
(250+x)/4=85 now cross multiply.
250+x=4*85
250+x=340
x=340-250
x=90 is the score required for the last test.
proof
(92+75+83+90)/4=85
340/4=85
85=85
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