A train covers a distance of 10 km in 12 minutes. If its speed is decreased by 5 km /hr, the time taken by it to cover the same distance will be :__________?
Correct answer: D. 13 min 20 sec
- A. 10 min
- B. 11 min 20 sec
- C. 13 min
- D. 13 min 20 sec
Explanation
The original speed is 10 km ÷ (12/60 h) = 50 km/h, so the reduced speed is 45 km/h. The new time is 10 km ÷ 45 km/h = 2/9 h = 13 min 20 sec; 13 min comes from rounding the recurring fraction too early.
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Problems relate distance, speed and time through the formula distance = speed × time, including unit conversion, average speed, relative speed and motion in opposite or the same direction. Questions may involve trains, boats and streams, where the effective speed changes, so average speed must not be confused with the simple average of two speeds.
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