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

A. 21 years
B. 18 years
C. 15 years
D. 9 years

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Explanation:

Let the ages of the three boys be 3x, 5x, and 7x, where x is a common factor.

According to the given information, the average age of the three boys is 15 years.

Average = (Sum of ages) / (Number of boys)

So, we have: 15 = (3x + 5x + 7x) / 3

Now, we can solve for x:
15 = (15x) / 3
15 * 3 = 15x
45 = 15x
x = 3

Now, we can find the age of the elder boy (7x):
Elder boy’s age = 7 * x = 7 * 3 = 21 years

Therefore, the age of the elder boy is 21 years.

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