The sum of a mother’s and son’s ages is (64) years. Four years ago, the mother’s age was (3) times the son’s age. What is the son’s present age?

Correct answer: 18

Let the present ages of the mother and son be \(x\) years and \(y\) years respectively. Then \(x+y=64\). From the condition four years ago, \(x-4=3(y-4)\). Substituting \(x=64-y\) gives \(60-y=3y-12\), so \(72=4y\) and \(y=18\). Hence, the son is presently 18 years old. Although 16 may be considered from the total, it does not satisfy the condition that the mother was three times the son's age four years ago. Exam tip: In age problems, subtract the same number of years from each person's present age for a past-age condition.