Question

A train m leaves city a at 5 am and reaches city b at 9:00 am . Another train n leaves city b at 7:00 am and reaches city a at 10:30 am. At what time do the 2 trains cross one another?

Answer 1

let dist. between A and B = X km.

for Train M time = 9am-5am =4hrs

speed of train m = (X/4)

for Train N time = 10.30-7 = 3.5 hrs = (7/2)hrs speed of train n = (X/3.5) = (2X/7)

dist . covered by train M before train N left.

=(x/4)* (5am-7am) = (X/4)*2 = (2X)/4 = X/2

DIS. LEFT =x/2

rel. speed =(X/4)+(2X/7) = 15X/28

time = (x/2)/(15x/28) = 5/6 hrs = 50 min. so the trains crossed at 7am +50min = 7.50am