The average age of three boys is 30 years and their ages are in the proportion 3 : 6 : 12. The age of the youngest boy is:	Choose the correct answer.
A) 21 years
B) 18 years
C) 15 years
D) 8.5 years
E) None of these
Total age of 3 boys = (30 Ã— 3) years = 90 years. Ratio of their ages = 3 : 6 : 12.   Age of the youngest = (60 Ã— 3â„21) years = 8.5 years.   Answer 8.5 years
<result>D</result>
The average age of three boys is 30 years and their ages are in the proportion 3 : 6 : 12. The age of the youngest boy is: