Multiple choice

Sunita travelled the first half of the distance from her home to office at a speed of 40 km/hr. For exactly one-third of the remaining distance, she travelled at 20 km/hr and the distance left after that at 10 km/hr. Find her average speed for the whole journey.

  1. 15.17 km/hr

  2. 16.23 km/hr

  3. 18.46 km/hr

  4. 14.28 km/hr

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let total distance be 6D. First half (3D) at 40 km/hr: time = 3D/40. Remaining 3D: 1/3 of remaining is D at 20 km/hr, time = D/20. Left is 2D at 10 km/hr, time = 2D/10. Total time = 3D/40 + D/20 + 2D/10 = (3D + 2D + 8D) / 40 = 13D/40. Average speed = 6D / (13D/40) = 240/13 = 18.46 km/hr.

AI explanation

Assume the total distance is 120 km, so the first half is 60 km, taking 60/40 = 1.5 hours. The remaining distance is 60 km, so one-third of it is 20 km, which takes 20/20 = 1 hour. The final distance of 40 km takes 40/10 = 4 hours. The average speed is total distance divided by total time: 120 divided by (1.5 + 1 + 4) equals 120/6.5, which is approximately 18.46 km/hr. The result is 18.46 km/hr.

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