Question : Three boys, on average, are 25 years old, and their ages are in the ratio of 3 : 5 : 7. What is the age of the youngest boy?
Option 1: 24 years
Option 2: 21 years
Option 3: 12 years
Option 4: 15 years
Correct Answer: 15 years
Solution :
The average age of the three boys is 25 years, which means the total age of the three boys is 25 × 3 = 75 years
Their ages are in the ratio 3 : 5 : 7.
The sum of the ratios is 3 + 5 + 7 = 15
Let the common factor be $x$.
So, the ages of the boys are $3x, 5x$ and $7x$.
The total age of the boys is equal to the sum of their ages.
$⇒3x + 5x + 7x = 75$
$\therefore x = 5$
Therefore, the age of the youngest boy = $3x$ = 3 × 5 = 15 years
Hence, the correct answer is 15 years.
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