2017 · Q12
If a train crosses a km-stone in 12 seconds, how long will it take to cross 91 km-stones completely if its speed is 60 km/hr ?
Elementary MathematicsTime, Speed and Distance
- A1 hr 30 min
- B1 hr 30 min 12 sec
- C1 hr 51 min
- D1 hr 1 min 3 sec
Explanation
At 60 km/h = 1 km/min, the train covers 0.2 km in 12 s — this is the train's length. Crossing 91 km-stones spans 90 km between the first and last stone, plus one train length (0.2 km) to clear the last stone: 90.2 km in all. At 60 km/h this takes 90.2 min = 1 hr 30 min 12 s. Hence option (B).