math
posted by Simon .
In a test, the average was 74 points/100 points. After the test, three of students relocate. Then the average was 75 points/100. The circumstances of the students were 6:5:3. How many points did the three students have?
I know the answere is 45, 75 and 90, but can you write the operation?

Mean = (sum of scores)/number of scores
If I understand your problem correctly, the ratio of the three scores are 6:5:3 and the mean of the three = 75. If that is what you are saying, then:
75 = (6x + 5x + 3x)/3 = 14x/3
14x = 225
Solve for x.
However, this does not give you the answers you indicate. Sorry. Can you state the problem more clearly?