Two persons are walking beside a railway track at respective speeds of 2 and 4 km per hour in the same directi

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. The time, in seconds, taken by the train to cross an electric post is nearest to

Select an option to reveal the answer and explanation

Accepted Answer

82. Let the length of the train be l k m s l kms l k m s and speed be s k m p h s kmph s k m p h . Base on the two scenarios presented, we obtain: l s − 2 = 90 3600 \frac{l}{s-2}=\frac{90}{3600} s − 2 l ​ = 3600 90 ​ ....(i) and l s − 4 = 100 3600 \frac{l}{s-4}=\frac{100}{3600} s − 4 l ​ = 3600 100 ​ ..