maths
posted by krishna .
the distance between two stations is 340 km two trains start simultaneously on parallel tracks to each other . the speed of one of them is greater than that of the other by 5 km/hr. if the distance between the two trains after 2 hrs of their start is 30 km , find the speed of each train

Two trains with speeds s and s+5 km/hr.
Initial distance=340 km
final distance = 30 km
Total distance travelled = 34030=310 km
Total speed = s+s+5=2s+5
Time = 2 hrs
Form equation equating distance travelled
Time*speed=distance, or
2(2s+5)=310
2s+5=155
2s=150
s=75
Speeds of trains are 75 km/h and 80 km/hr 
If one train has a velocity of V km/h, the other one will have velocity V+5 km/h approaching the first train. Therefore Relative velocity will be V+V+5=2V+5 km/h.
Distance travelled by them in 2 hrs is 34030=310km which is =2(2V+5)
Thus 4V+10=310 or 4V=300 hence V=75km/h and other train has a velocity of 80km/h.
Check: in 2 hrs they will move 75x2+80x2=150+160=310km =34030 km. OK.