The average age of three boys is 15 years and their ages are in the proportion 3 : 5 : 7 . What is the age in years of the youngest boy? - Quantitative Aptitude MCQ Competitive Examination 2026 | ExamTest.live

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

Solution & Step-by-step Explanation

Let the ages of the three boys be 3 x, 5 x, and 7 x . The average age is given as 15 years. Average = \frac{3 x + 5 x + 7 x}{3} = 15 \frac{15 x}{3} = 15 ⟹ 5 x = 15 ⟹ x = 3 The age of the youngest boy is: Age = 3 x = 3 \times 3 = 9 years

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

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9

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21

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