Question 971751
mean = total/number

total= mean * number
total = 83*40 = 3320
But class of 25 had a mean of 80, so their total was 2000.

There are 15 in the other class, and their total had to be 1320.

The mean in the other class is 1320/15.

It equals 88.

Mean of class 1 was 80; class 2, smaller, had a mean of 88.  The combined mean should be weighted closer to class 1, and it is.