5 students are in a maths class and 10 students are in a physics class. The mean mark of the maths class is 90 and the mean mark of the physics class is 85. Work out the mean mark of both classes.

To find the mean mark the formula is mean = ∑marks /number of students Therefore the mean for maths is 90 and so ∑marks = meannumber of students = 905 = 450 and the ∑marks for the physics class is 85*10= 850. Therefore total number of marks is 450 + 850 = 1300. Then the mean of both sets of data is the total number of marks divided by total number of students. Total number of students = 10+5 = 15; therefore the mean of both sets of data is 1300/15 = 86.7 (to 3 s.f.)