Multiple choice

A boy covers a certain distance on a toy train. If the train moved 4 kmph faster, it would take 30 minutes less. If it moved 2 kmph slower, it would take 20 minutes more. The distance is

  1. 40 km

  2. 50 km

  3. 60 km

  4. 80 km
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let distance be D and speed be S. D/S - D/(S+4) = 0.5 and D/(S-2) - D/S = 1/3. Solving this system: D = S(S+4)/8 and D = S(S-2)/6. Equating: 6S(S+4) = 8S(S-2) -> 6S+24 = 8S-16 -> 2S=40 -> S=20. D = 20(24)/8 = 60.

AI explanation

Let the distance be D and the original speed be S. The equations are D/S minus D/(S + 4) = 0.5 and D/(S minus 2) minus D/S = 1/3. Multiplying the first equation by (S)(S+4) and the second by (S)(S-2), we get 4D = 0.5(S squared + 4S) and 2D = S squared / 3 minus 2S / 3. Solving these yields S = 20 kmph and D = 60 km.

Keep practicing — related questions