There are four people in a family. The average age of these four members is 32 years. The father's age is 50 years, the mother's age is 46 years, and the daughter's age is 20 years. Find the age of the only son in the family.

Let's assume the present ages of father, mother, son and daughter is 'F', 'M', 'S' and 'D' respectively.

The average age of these four members is 32 years.

average age of these four members = $$\frac{F+M+S+D}{4} = 32$$

F+M+S+D = 128

The father's age is 50 years, the mother's age is 46 years, and the daughter's age is 20 years.

50+46+S+20 = 128

116+S = 128

S = 128-116

Age of the only son in the family = 12 years