3 trains leave a station at the intervals of half hour. The third train after travelling for 1 hour, meets the second train but this was half hour after it meets the first train. Calculate the speed of the second train relative to the first if the distance between the meeting points is 30 km.
1. 15 kmph
2. 20 kmph
3. 25 kmph
4. 40 kmph
Distance traveled by the third train in 1 hour = Distance traveled by second train in 1 & half hour ---- 1
Distance traveled by the first train in 1 & half hour = Distance traveled by third train in half hour ---- 2
The third train covers 30 km in half hour.
Speed of third train = 60 kmph
Using 1, the second train covers 60 km in 1 and half hour.
Speed of second train = (60/1.5) = 40 kmph.
Using 2, the first train covers 30 km in 1 and half hour.
Speed of first train = (30/1.5) = 20 kmph.
Relative speed of second train = 40 - 20 = 20 kmph. Hence (2)