The average age of three boys is 25 years and their ages are in the proportion 3 : 5 : 7. The age of the youngest boy is Choose the correct choice from the following:
A) 9 years
B) 15 years
C) 18 years
D) 21 years
E) None
Sol.   Total age of 3 boys = (25 x 3) years = 75 years.   Ratio of their ages = 3 : 5 : 7.   Age of the youngest = (75 x 3/15)years = 15 years.   Answer 15 years
<result>B</result>
The average age of three boys is 25 years and their ages are in the proportion 3 : 5 : 7. The age of the youngest boy is