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

  • 21 years
  • 18 years
  • 15 years
  • 9 years
  • 12 years

Let’s denote the ages of the three boys as 3x, 5x, and 7x, where x is a common factor. The ratio of their ages is given as 3:5:7.

The average age of the three boys is given as 15 years. The average is calculated by adding up the ages and dividing by the number of boys.

 

Average=Sum of AgesNumber of Boys

In this case, the sum of their ages is

3x+5x+7x=15x and there are three boys. 

15=15x3

Now, solving for x:

15=5x

x=3Now that we have the value of x, we can find the ages of the three boys:

Age of the youngest boy:

3x=3×3=9 years.

Therefore, the age of the youngest boy is 9 years.

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