The average age of 3 boys is 20 years and their ages are in the proportion 3:5:7. The age of the youngest boy is?
Pick.
A) 10years
B) 15years
C) 20years
D) 25years
E) 12years
Total age of 3 boys = 20*3= 
<gadget id="calculator">20*3</gadget>
<output>60</output>
60   ratio of their ages= 3:5:7   Age of the youngest = 60*3/15= 
<gadget id="calculator">60*3/15</gadget>
<output>12</output>
12 years   Answer is 12years
<result>E</result>
The average age of 3 boys is 20 years and their ages are in the proportion 3:5:7. The age of the youngest boy is?