Algebra
posted by Kahlil on .
Ms Newton's class took the same test as Mr. Euclid's students. Ms. Newton's class has 20 students, and the average(mean) test score was 90. The average of Mr. Euclids class was 80. If you combine both classes the average score on the test is 85. How many students does Mr. Euclid have in his Mathematics class?

If Newton had 20 students and Euclid had e students,
total points = 20*90 + e*80
total students = 20+e
total average = (20*90 + e*80)/(20+e) = 85
1800 + 80e = 1700 + 85e
100 = 5e
e = 20
Makes sense. 85 is halfway between 80 and 90, so there must have bee the same number of students in each class. 
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