Question

A boy was born on his father's 30th birthday. The sum of their ages is now 40 years. How old is the boy?

Answer 1

A boy was born on his father's 30th birthday. The sum of their ages is now 40 years. How old is the boy?

Solution:

Assume that the age of the boy is $x$.

The age of the father is $30 + x$. The sum of their ages is $x + x + 30 = 40$

$$2x = 40 - 30$$ $$2x = 10$$ $$x = 5$$

Answer: age of the boy is 5.