Multiple choice

The average age of 3 boys is 15 years. If the ratio of their ages is 3 : 5 : 7, what is the age of the youngest boy?

  1. 9 years

  2. 12 years

  3. 18 years

  4. 21 years
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A Correct answer
Explanation

The sum of ages is 3 * 15 = 45. The ratio is 3:5:7, so 3x + 5x + 7x = 15x = 45, which means x = 3. The youngest boy is 3x = 3 * 3 = 9 years.

AI explanation

Using the average formula, the total age of the 3 boys is 3 multiplied by 15, giving 45 years. Let their ages be 3x, 5x, and 7x based on the given ratio, so their sum is 15x. Setting 15x equal to 45 gives x = 3. The age of the youngest boy is 3x, which calculates to 9 years.

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