Average age of mother and father is 28 years. Average age of mother, father and their child is 20 years. What is the age of child?

4 years 3 years 6 years 5 years

4 years

Sum of age of father & mother = 2 × 28 = 56 years Sum of age of mother , father & child = 3 × 20 = 60 years Age of child = 60 - 56 = 4 years