Q33.A teacher gave the same test to three history classes: A, B, and C. The average (arithmetic mean) scores for the three classes were 65, 80, and 77, respectively. The ratio of the numbers of students in each class who took the test was 4 to 6 to 5, respectively. What was the average score for the three classes combined?
A. 74
B. 75
C. 76
D. 77
E. 78
答案是B
不好意思,我看这题没人问过,想必是个简单题,但是我还是得不出75,请哪位指正一下我的思路!谢谢! | 
