The sum of the ages of 5 children born at intervals of 3 years each is 50 years. What is the age of the youngest child ?

4 years 

Let the age of the youngest child be x – 6 yrs.

So ages of the other 5 children would be: x – 3, x, x + 3 and x + 6.

ATQ, x – 6 + x – 3 + x + x + 3 + x + 6 = 50

x = 10

So the age of the youngest child will be 10 – 6 = 4 years.