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? 

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JKSSB SI Official Paper (Held On: 11 Dec 2022 Shift 2)
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  1. 9 years
  2. 11 years
  3. 6 years
  4. 10 years

Answer (Detailed Solution Below)

Option 1 : 9 years
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Detailed Solution

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Given:

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

Formula used:

Average = Total sum of ages / Number of boys

Calculations:

Let the ages of the boys be 3x, 5x, and 7x.

Average age = 15

⇒ (3x + 5x + 7x) / 3 = 15

⇒ 15x / 3 = 15

⇒ 5x = 15

⇒ x = 3

⇒ The age of the youngest boy = 3x = 3 × 3 = 9 years

∴ The correct answer is option 1.

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