A train runs at a speed of 90 km/h in the first 10 min, 60 km/h in the next 20 min, and 40 km/h in the last 5 minutes. What is the average speed (in km/h) of the train?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is Option 4 i.e..
Speed = 90 km/h.
Time = 10 min = (10/60) = 1/6 hour.
Distance Covered = S × T = 90 × (1/6) = 15 km.
Speed = 60 km/h.
Time = 20 min = (20/60) = 1/3 hour.
Distance Covered = S × T = 60 × (1/3) = 20 km.
Speed = 40 km/h.
Time = 5 min = (5/60) = 1/12 hour.
Distance Covered = S × T = 40 × (1/12) = 10/3 km.
Total Distance covered = 20 + 15 + 10/3 = 115/3 km.
⇒ Total Time = 20min + 10min + 5min = 35min = (35/60) = (7/12) Hour.
So,
Average Speed = (115/3) ÷ (7/12) = 460/7 = kmph