Three years ago, the age of C was three times that of D. Four years from now, the age of C will be twice that of D. What is the present age of C?

Correct answer: 24. Let C = c and D = d. Then c − 3 = 3(d − 3) and c + 4 = 2(d + 4). Solving gives d = 10 and c = 24.

Background: Check: 3 years ago C = 21 and D = 7 (21 = 3 × 7); in 4 years C = 28 and D = 14 (28 = 2 × 14).

• 20: 20 does not satisfy both conditions.
• 26: 26 does not satisfy both conditions.
• 28: 28 does not satisfy both conditions.

Did you know? Make equations for “ago” and “later” separately.

Memory trick: Write ago and later equations.