Multiple choice

The ratio of the ages of two boys is 3 : 4. After 3 years, the ratio will be 4 : 5. After 21 years, the ratio of their ages 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. (3x+3)/(4x+3) = 4/5. 15x + 15 = 16x + 12. x = 3. Current ages are 9 and 12. After 21 years, ages are 30 and 33. Ratio = 30/33 = 10/11.

AI explanation

Let the present ages of the two boys be 3x and 4x respectively. After 3 years the ratio gives (3x + 3) / (4x + 3) = 4 / 5, which cross-multiplies to 15x + 15 = 16x + 12, yielding x = 3. Their present ages are 9 and 12, so after 21 years their ages will be 30 and 33, giving a ratio of 10 : 11.