The average age of three boys is 5 years and their ages are in proportion 3:5:7. What is the age in years of the youngest boy?
Choose the correct answer:
A) 1 B) 2 C) 3 D) 4 E) 5
3x + 5x + 7x = 15   x 3  + 5  + 7= 
<gadget id="calculator">3  + 5  + 7</gadget>
<output>15</output>
15   x=1   3x = 3   ANSWER:3
<result>C</result>
The average age of three boys is 5 years and their ages are in proportion 3:5:7. What is the age in years of the youngest boy?