Answer:
The sum of age of the two new boys = 56 years
Step-by-step explanation:
The average age of a group of 13 boys = 13
The sum of age of the 13 boys = 13 * 13 = 169
The average age of a group of 15 boys = 15
The sum of age of the 15 boys = 15 * 15 = 225
The sum of age of the two new boys = 225 - 169 = 56 years