Problem 4 of 25sta-004
A class of 30 students has a mean score of 70 on a test. A second class of 20 students has a mean score of 80 on the same test. What is the mean score of all 50 students?
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Solution walkthrough1:48
- The classes are different sizes, so find the mean from scratch: all the points divided by all the students.
- Total mean count. First class: . Second class: .
- Together: points, shared by students.
- Combined mean: .
- Check: is the balance point. on one side and on the other.
- Traps: ignores the class sizes, swaps them, and is only the first class.