Three years ago the average of a family of five members was 17 years. A baby having been born the average age of the family is the same today. Find the age of the child.

2 year

 3 years ago , Total age of family of 5 members = 17× 5 = 85 years 

Sum of present age of 5 members = 85 + 5 × 3= 100 years 

but a baby born and average age of present age of 6 members remains same i.e. 17 years 

Sum of present age of 6 members =  17 × 6= 102 years 

Age of baby = 102 - 100 = 2 years