Answer:
21.5 to 1 decimal place.
Explanation:
The total number of marks for all the boys = 28*28 = 784 marks.
The total number of marks for all the girls = 24*14 = 336 marks.
So the mean mark for the whole group
= (784+336) / (28+24)
= 1120 / 52
= 21.538