The average weight of 20 students in a class is 52 kg.

Solution

Total weight of 20 students = 20 X 52 = 1040 kg Total weight of 2 students who left the class = 2 X 40 = 80 kg So, the total weight of 18 remaining students = 1040 - 80 = 960 kg Let the average weight of the 6 new students who joined the class be 'y' kg So, new total weight after 6 new students joined the class = 960 + 6 X y = (960 + 6y) kg New total number of students = 20 - 2 + 6 = 24 New average weight of the 24 students = 52 - 0.75 = 51.25 kg So, we have, (960 + 6y) = 24 X 51.25 Or, 960 + 6y = 1230 So, y = (1230 - 960) ÷ 6 Or, y = 45