SOLUTION: Roberto finds that the score he achieves on a math exam varies directly with the average amount of time (in minutes) he spends studying after class. After studying an average of 90

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Question 218764: Roberto finds that the score he achieves on a math exam varies directly with the average amount of time (in minutes) he spends studying after class. After studying an average of 90 minutes, his score was 72. What will his score be if he increases the amount of time to an average of 100 minutes.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
This is a ratio problem
Let t = time in minutes spent studying after class
Let s = score in exam
It's a direct variation, so
s+=+k%2At
Where k is a constant
given:
72+=+k%2A90
k+=+.8
---------------
s+=+k%2A100
s+=+.8%2A100
s+=+80
His score will be 80 with 100 minutes of study