Aptitude - Problems on Trains - Discussion

The correct option is B: 10 A.M.

We know, Time = Distance/speed.

Here, we have to consider the relative speed of two trains.

=> 20 km/hr + 25 km/hr = 45 km/hr (since they are moving in opposite directions)

Here, the distance between them cannot be taken as 110 km as train B didn't start at 7 A.M.

The distance train A would have covered from 7 A.M to 8 A.M will be =
20km/hr* 1hr= 20 km.

So, the distance between these two trains will become 110 km - 20 km = 90 km at 8 A.M.

So now, the time is taken for them to meet = 90 km/ 45 km/hr= 2 hrs.

They meet 2 hrs after 8 A.M i.e 10 A.M.

As A train starts at 7 am at 20kmph and B starts at 8 am at 25kmph.

The distance between them is 110 km.

As A starts an hour early at 8 am, A has travelled 20 km.

Now at 8 am, the distance between them is 110–20 km.

As of now, we have a distance as 90 km.
The relative speed is 45kmph.

Time = Distance/Speed.
Time = 90/45 = 2 hrs.
i.e after 2 hours, so 8 a.m + 2 hours = 10 a.m.

As A train starts at 7 am at 20kmph and B starts at 8 am at 25kmph.

The distance between them is 110km.
As A starts an hour early at 8 am A has travelled 20 km.
Now at 8 am distance between them is (110-20)km.
As of now we have a distance as 90km.
The relative speed is 45kmph.
Time = Distance/Speed.
Time = 90/45 =2 hrs.

To solve this we can take a very simple approach.
As we have total distance between them 110 km and A is starting at 7 a.m.
So after 1 hr that is at 8 a.m he will cover 20 km so;
110-20 = 90km.

Now for both the trains we have 90 km and starting at 8 a.m so we can find there crossing time, as they will cross each other
T = d / s(a train ) + s (b train).
T = 90/ (20 + 25),
T = 90/ 45 = 2 hrs,
i.e after 2 hrs so 8 a.m + 2hrs = 10 a.m.

My logic answer:

At 7, distance covered, A =0 km, B = 0 km.
At 8, distance covered A = 20 km, B =0 km.
At 9, distance covered A = 40 km, B = 25 km.
At 10, distance covered, A = 60 km, B = 50 km.
At 11, distance covered, A = 80 km, B = 75 Km.
At 12, distance covered, A =100 Km, B = 100 k.

Correct me, if my logic is wrong.

It's very interesting and useful to learn. Thanks.

I didn't get anything. Please help me to get this.

Tell me that these two trains meet at what distance. Please anyone explain to me.

2 station A and B are 110km apart.
1 train start from A at 7 am towards B at 20 kmph 110-20 = 90.

Next one start from B at 8 a.m towards A at 25kmph.
20+25 =45.

Now 90/45 = 2hrs.
.`. 8+2 = 10 a.m.

Hey @Syed.

x-1 is used because the second train starts one hour after the first train.

When X=3 is the time in hours to meet. The starting time is 7 a.m so add 3 to it is 10 a.m when the trains meet.