Multiple choice

A train travelling with uniform speed crosses two bridges of lengths 300 m and 240 m in 21 seconds and 18 seconds respectively. The speed of the train is

  1. 72 km/hr

  2. 68 km/hr

  3. 65 km/hr

  4. 60 km/hr
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A Correct answer
Explanation

Let train length = L meters and speed = v m/s. For bridge 1: L+300 = 21v. For bridge 2: L+240 = 18v. Subtracting: 60 = 3v, so v = 20 m/s = 20 × 18/5 = 72 km/hr. The answer is derived by solving the two simultaneous equations.

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