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?

Algebra 
Steve,
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. 
Algebra 
Daniel,
Luisa mows lawns during the summer. She charges $15 if she cuts the grass but charges $5 more if she also trims the grass. Last week she trimmed 5 more yards than she cut. If she made $415 last week, how many yards did she trim?