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
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Last update on October 11, 2:29 am by Rahil Choudhary.
The time taken by 3rd train and 2nd train are 1 hr and 1.5 hr respectively.
So speed will be in the ratio 3:2
Now the time taken by 1st and 3rd train are in the ratio 1.5 hr and 0.5 hr so 3:1 hence their speed ratio will be 1:3 henc
Speed ratio of 1st 2nd 3rd
1 : 2 :3
Now 3rd train covers 30 km in 1/2 hr so speed in 60kmph
Hence 2-1 represent the relative speed =10 which is equivalent to 20kmph
For train1,
D=1.5S1
For Train3,
D=0.5S3
Now meeting of train 2 and 3,
D+30=S3
D+30=1.5S2
Put the equations,
0.5S3+30=S3
1.5S1+30=1.5S2
=» 30=1.5(S2-S1)
=»S2-S1=30/1.5
Therefore, answer is 20kmph
Ans(2)
Answer is 20 kmph
Consider distance travelled by 1st train in one and half hour = distance travelled by 3rd train in half hour
Similarly, distance travelled by 3rd train in 1hr = distance travelled by 2nd train in one and half hour
3rd train covers 30 km in half hr
Speed = 60
So 2nd train covers 60 km in one and half hr. Hence speed=60/1.5=40
Similarly speed of 1st train is 20.
Relative speed of second would be 40-20=20kmph
Hi Simran. You need to explain your answer to win points.
Okk sir, by mistake in a hush i marked option 1 as i thought it is 20kmph but i read it now clearly
But now i have given the explanation and correct answer also...
Sorry for this...
Let train 1 = t1; train 2 =t2; train 3 =t3
T3 in 1 hr will meet T2 when T2 travels for 1 and half hr
T3 in half an hour will meet T1 when T1 travels for 1 and half hr
As per given data,
T3 cover 30 Km in half hr
Hence T3 speed = 60 kmph
Similarly, T2 travels 60 km in 1 and half hr
Hence T2 speed = 40 kmph
T1 travels 30 km in 1 and half hr
T1 speed = 20 kmph
Relative speed of T2 from T1 = 20 kmph
Answer: 2) 20 kmph
Let train 1 = t1; train 2 =t2; train 3 =t3
When T3 travels 1 hr it meets T2, where T2 has already traveled for 1 and half hr
When T1 travels for one and half hour it meets T3, where T3 has already traveled for half an hr
From given observations,
T3 cover 30 Km in half hr
T3 Speed (x3) = 2 *30 = 60 kmph
Using x3; T2 Speed (x2) = (60/1.5) = 40 kmph
Using x2; T1 Speed (x1) = (30/1.5) = 20 kmph
Relative speed T2 - T1 = 20 kmph