Question

Mr Flannery's math class averaged poorly on a test, so he gave them a retest. There are 30 students in his class. On the retest, 10 students gained 15 points each, 10 students gained 5 points each, and 10 students lost 5 points each. How does the MEAN of the retest scores compare to the MEAN of the scores on the first test?
A)
The means are the same.


B)
The mean on the retest is 5 points higher.


C)
The mean on the retest is 10 points higher.


D)
The mean on the retest is 15 points higher.

Answer 1

Overall the class added 150 points (10×15) to the total class points.
The points earned from the 10 who increased by 5 (50pts) was erased by those 10 who lost 5pts each (50points)

150/30 is 5. The class average or mean went up 5 points after the retake

Answer 2

Answer:

The mean on the retest is 5 points higher. The increase in the total of all the scores is 10(15) + 10(5) - 10(5) = 150, so the mean increases by 150/30 = 5.