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 option:	A) 21 years	B) 18 years	C) 15 years	D) 9 years	E) None of these
Total age of 3 boys = (25 × 3) years = 75 years. Ratio of their ages = 3 : 5 : 7.   Age of the youngest = (75 × 3⁄15) years = 15 years.   Answer 15 years
<result>C</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: