1.

A train passes two persons walking in the same direction at a speed of 3 km/hr and 5 km/hr respectively in 10 seconds and 11 seconds. The speed of the train is (a) 28 km/hr (b) 27 km/hr (c) 25 km/hr (d) 24 km/hr

Answer»

 (c) 25 km/hr

Distance covered by the first person in 10 seconds = \(\bigg[\bigg(3\times\frac{5}{18}\bigg)\times10\bigg]\) m = \(\frac{25}{3}\) m 

Distance covered by the second person in 11 seconds =  \(\bigg[\bigg(5\times\frac{5}{18}\bigg)\times11\bigg]\) m = \(\frac{275}{18}\) m 

∴ The train travels a distance = \(\frac{275}{18} - \frac{25}{3}= \frac{128}{8}\) m in (11 – 10) = 1 second.

∴ Speed of the train = \(\bigg(\frac{125}{18}\times\frac{18}{5}\bigg)\) km/hr = 25 km/hr.



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