A train when moves at an average speed of 60 kmph, reaches its destination on time. When its average speed becomes 45 kmph, then it reaches its destination 30 minutes late. Find the length of journey.
Solution: Difference between timings = 30 min. = 30/60 hr = 1/2 hr.
Let the length of the journey be x km.
Then, x/45 - x/60 = 1/2
=> 4x -3x = 180/2
=> x = 90 km.
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