Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 30)
30.
Two stations A and B are 110 km apart on a straight line. One train starts from A at 7 a.m. and travels towards B at 20 kmph. Another train starts from B at 8 a.m. and travels towards A at a speed of 25 kmph. At what time will they meet?
Answer: Option
Explanation:
Suppose they meet x hours after 7 a.m.
Distance covered by A in x hours = 20x km.
Distance covered by B in (x - 1) hours = 25(x - 1) km.
20x + 25(x - 1) = 110
45x = 135
x = 3.
So, they meet at 10 a.m.
Discussion:
92 comments Page 9 of 10.
Poojitha said:
1 decade ago
How is it 20x+25(x-1) = 110?
Shri said:
2 decades ago
Why (x-1) term is used ?
Rambabu said:
1 decade ago
@Easwar.
Distance is x and speed first train is = x/6 (because speed=distance/time).
And speed of train second train is = x/3.
First train start at 5pm. If it travel two hours up to 7pm, the distance covered by this train is ( (x/6) *2) is x/3 and the remaining distance is (x- (x/3) is 2x/3.
Now find relative speed (opp direction) is (x/6) + (x/3) =x/2.
Remaining distance is 2x/3 and relative speed is x/2 so,
( (2x/3) / (x/2) ) = 4/3hours.
Means after 7 pm both trains meet at 4/3 hours later. (4/3) *60=80 minutes so at 8:20 pm both trains meet.
Thank you.
Distance is x and speed first train is = x/6 (because speed=distance/time).
And speed of train second train is = x/3.
First train start at 5pm. If it travel two hours up to 7pm, the distance covered by this train is ( (x/6) *2) is x/3 and the remaining distance is (x- (x/3) is 2x/3.
Now find relative speed (opp direction) is (x/6) + (x/3) =x/2.
Remaining distance is 2x/3 and relative speed is x/2 so,
( (2x/3) / (x/2) ) = 4/3hours.
Means after 7 pm both trains meet at 4/3 hours later. (4/3) *60=80 minutes so at 8:20 pm both trains meet.
Thank you.
Baswaraj said:
1 decade ago
So x = 3.
Then B start 7 a.m so count three numbers like 8,9,10 (after 7 we will get 8) :10 a.m.
Then B start 7 a.m so count three numbers like 8,9,10 (after 7 we will get 8) :10 a.m.
Govinda said:
1 decade ago
Its very simple.
Train A start at 7 AM & B start at 8 AM. A travels 20 km in 1 hr ie, distance between A and B will be.
90 Km at 8 AM.
Relative speed = 20+25 = 45Km/hr.
Distance = 90km.
Time = 90/45 = 2 hr.
Total time = 2+1 (that was travelled by train A between 7 to 8 AM. ).
Answer will be 7+3 = 10 AM.
Train A start at 7 AM & B start at 8 AM. A travels 20 km in 1 hr ie, distance between A and B will be.
90 Km at 8 AM.
Relative speed = 20+25 = 45Km/hr.
Distance = 90km.
Time = 90/45 = 2 hr.
Total time = 2+1 (that was travelled by train A between 7 to 8 AM. ).
Answer will be 7+3 = 10 AM.
Gandhi said:
1 decade ago
Who ever doesn't understand why they have taken (X-1). Please see the below example.
Length of the track between starting position of train A starts at 7A.M and B Starts at 8A.M is 200 km.
Let's say A train travels with 20 kmph for 5 hours.
Distance covered by train A is = 100 km.
Train B Travels with 25 kmph for 4 hrs.
Distance covered by train B is =100km.
A train => 7+5=12 noon.
B train => 8+4=12 noon.
If we consider 7 as X then 8 should become (X-1) when we compare with the destination time.
Length of the track between starting position of train A starts at 7A.M and B Starts at 8A.M is 200 km.
Let's say A train travels with 20 kmph for 5 hours.
Distance covered by train A is = 100 km.
Train B Travels with 25 kmph for 4 hrs.
Distance covered by train B is =100km.
A train => 7+5=12 noon.
B train => 8+4=12 noon.
If we consider 7 as X then 8 should become (X-1) when we compare with the destination time.
Manish Dabhi said:
1 decade ago
Train A Travel in 1 hour 20 km at 7 am.
They both started together 8 am.
That's why 110-20 = 90km Remaining,
Relative Speed = (20+25) = 45 km/hr.
Time = (Distance/Speed).
= (90/45)
= 2 Hours
That's why 8am + 2 hours = 10 am.
They both started together 8 am.
That's why 110-20 = 90km Remaining,
Relative Speed = (20+25) = 45 km/hr.
Time = (Distance/Speed).
= (90/45)
= 2 Hours
That's why 8am + 2 hours = 10 am.
Bhoopesh Choudhary said:
1 decade ago
The answer of this question is incorrect if the B train start at 8am and by the speed 25km\hr then it will cover the distance of 50km in next 2 hours but the train A will cove the distance of 60km in next 3 hour by the peed of 20km\hr.
So both can be meet at 10 a.m.
So both can be meet at 10 a.m.
Charles @ Redhills said:
1 decade ago
@Joicy.
The train B starts an hour later than the train A. Thus the train time A is assumed as x (started at 7 am) and the train B starts at time 8 am which is later an hour of time x hence its x-1. Hope its clear to you now.
The train B starts an hour later than the train A. Thus the train time A is assumed as x (started at 7 am) and the train B starts at time 8 am which is later an hour of time x hence its x-1. Hope its clear to you now.
Joicy said:
1 decade ago
Why (X-1) term is used?
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