Multiple choice

The ratio of the ages of two girls is 3: 4. After 3 years, the ratio will be 4: 5. The ratio of their ages after 21 years will be

  1. $14: 17$
  2. $17: 19$
  3. $11: 12$
  4. $10: 11$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let ages be 3x and 4x. After 3 years: (3x + 3)/(4x + 3) = 4/5. Cross-multiplying: 15x + 15 = 16x + 12, giving x = 3. Current ages: 9 and 12. After 21 years: (9 + 21)/(12 + 21) = 30/33 = 10/11. Ratio is 10:11.