Answer:
14.8 years
Explanation:
Average age = total age / number of boys
Average age of ten boys = total age for 10 boys/ 10
Average age of 9 boys (15) = total age for 9 boys/ 9
total age for 9 boys = 9 * 15 = 135
total age for 10 boys = total age for 9 boys + 13 = 135+13 = 148
Average age of ten boys = 148/ 10 = 14.8 years