Two classes, one with 15 students and the other with 25 students, took the same test and averaged 85 points and 75 points, respectively. If the two classes were combined, the overall average score of the 40 students would be 80 points.

The combined average can be calculated by finding the total points scored by both classes and then dividing by the total number of students. For the class of 15 students with an average of 85 points, the total points scored would be 15 * 85 = 1275. For the class of 25 students with an average of 75 points, the total points scored would be 25 * 75 = 1875. The combined total points for both classes is 1275 + 1875 = 3150. Dividing this by the total number of students (40) gives an overall average score of 3150 / 40 = 78.75, not 80.