SOLUTION: On an achievement test, ninth graders averaged 93% and eigth graders averaged 75%. A total of 90 students took the test and averaged 87%. How many ninth graders took the test?

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Question 71776: On an achievement test, ninth graders averaged 93% and eigth graders averaged 75%. A total of 90 students took the test and averaged 87%. How many ninth graders took the test?
Answer by checkley75(3666) About Me  (Show Source):
You can put this solution on YOUR website!
.93X+.75(90-X)=.87*90
.93X+67.5-.75X=78.3
.18X=78.3-67.5
.18X=10.8
X=10.8/.18
X=60 ANSWER FOR THE NUMBER OF NINTH GRADERS WHO TOOK THE TEST.
PROOF
.93*60+.75*30=78.3
55.8+22.5=78.3
78.3=78.3