The average age of three boys is 15 years.if their ages are in the ratio 3: 5: 7, the age of the youngest boys is?

3 year
15 year
18 year
21 year

Correct Answer: 3 year

Explanation:

Age of A : age of B : age of C = 3 : 5 : 7
So the average age of 3 boys (3x + 5x + 7x ) /3 = 15
⇒15x= 15 x 3
∴ x= 3

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