The average age of three boys is 15 years and their ages are in proportion 3:5:7

Question

The average age of three boys is 15 years and their ages are in proportion 3:5:7. What is the age in years of the youngest boy?

Options:

A . 15

B . 9

C . 18

D . 21

Answer: Option B
3X + 5X + 7X = 45
X =3
3X = 9

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