GIVEN: Length of the train = 240 m FORMULA: Length of the train = (Time taken to cross a man walking in the same direction) × (Speed of the train - Speed of the man) CALCULATION: Let the speed of the train be v km per hour Speed of train with respect to the walking man =(v−8)×(
5
18
) ⇒
(5v−40)
18
-----(1) Speed of train with respect to the running man =(v+10)×(
5
18
) ⇒
(5v+50)
18
------(2) According to the question and from (1) [240÷{
(5v−40)
18
}]=12 ⇒240×18=12×(5v−40) ⇒ v – 8 = 72 ⇒ v = 80 km per hour Now, The required time to cross the running man =