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

Solution:
Sum of ages of three boys = 45 years
Now, (3x + 5x + 7x) = 45
⇒ 15x = 45
⇒ x = 3
So, age of youngest boy = 3x
= 3 × 3
= 9 years

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