A train covers a distance in 100 min , if it runs at a speed of 48 kmph on an…
2023
A train covers a distance in 100 min , if it runs at a speed of 48 kmph on an average . The speed at which the train must run to reduce the time of journey to 40 min will be -
- A.
90 kmph
- B.
110 kmph
- C.
100 kmph
- D.
120 kmph
Attempted by 15 students.
Show answer & explanation
Correct answer: D
Key idea: find the distance from the initial speed and time, then compute the required speed for the new time.
Convert 100 minutes to hours: 100/60 = 5/3 hours.
Compute the distance: distance = speed × time = 48 × (5/3) = 80 km.
Convert 40 minutes to hours: 40/60 = 2/3 hours.
Required speed = distance / time = 80 / (2/3) = 120 kmph.
Quick check:
At 100 km/h: time = 80/100 = 0.8 h = 48 min (too long).
At 110 km/h: time = 80/110 ≈ 0.7273 h ≈ 43.64 min (still > 40).
At 120 km/h: time = 80/120 = 2/3 h = 40 min (meets the requirement).