CAT 2020 Slot 1 QA Question 5: Two persons are walking beside a railway track at respective speeds of 2 and 4 km per hour in the same direction. A train came from behind them and crossed them in 90 and 100 seconds, respectively. T

Question

Two persons are walking beside a railway track at respective speeds of 2 and 4 km per hour in the same direction. A train came from behind them and crossed them in 90 and 100 seconds, respectively. T

Accepted Answer

Let the speed of the train be $v$ km/hr and its length be $L$ km. Since the train comes from behind, we use relative speed.

$\dfrac{L}{v - 2} = \dfrac{90}{3600}$
$\dfrac{L}{v - 4} = \dfrac{100}{3600}$

Dividing the first equation by the second equation,

$\dfrac{v - 4}{v - 2} = \dfrac{90}{100} = \d

Two persons are walking beside a railway track at respective speeds of 2 and 4 km per hour in the same direction. A train came from behind them and crossed them in 90 and 100 seconds, respectively. The time, in seconds, taken by the train to cross an electric post is nearest to