Answer:
15.6
Explanation:
First, multiply the midpoint of each class by its frequency, as follows:
Class midpoint frequency midpoint*frequency
0-9 4.5 24 4.5*24 = 108
10-19 14.5 20 14.5*20 = 290
20-29 24.5 32 24.5*32 = 784
Total 76 1182
The mean is computed as the division between the addition of the "midpoint*frequency" column by the addition of "frequency" column.
mean = 1182/76 ≈ 15.6