Two trains approach each other at 25 km/hr and 30 km/hr respectively from two points A and B. Second Train travels 20 km more than first. What is the distance between A and B ?
My approach:
Since Distance=Speed⋅Time
[I just added the time it took to cover the distance taken by the Second train(30 km/hr) to cover 20 km to the First train(25 km/hr) to get distance as constant]
(First Train)
For 20 km at 25 km/hr, the time taken would be
time =2025=45
So First train taken would take 4/5 time more to cover the distance d
d=25⋅(t+4/5) ---> (1)
d=30⋅t ---> (2)
Now since distance is constant and speed is inversely proportional to time,
Ratio of speeds =2530=56
Ratio of times =t+4/5t=5t+45t=5t+45t
So
56=5t+45t
Since it is inversely proportional
5(5t+4)=6(5t)
25t+20=30t
25t−30t=−20
−5t=−20
t=4
So applying t=4 in (2)
d=30⋅4=120 km but its wrong
The correct answer is 220 km
I don't understand! help
Answer
I think best way to describe all the data is in a table like this
VTDTrain 125[kmh]Train 230[kmh]
Denote the distance the first train traveled until the meeting
by x. Therefore the second train traveled x+20. Lets add this
to the table:
VTDTrain 125[kmh]x[km]Train 230[kmh]x+20[km]
Now we can complete our table using that T=DV
VTDTrain 125[kmh]25x[h]x[km]Train 230[kmh]30x+20[h]x+20[km]
Assuming both trains left both points at the same time we get that
T1=T2 where T1,T2 is the time travel for each train
until the meeting. So
25x=30x+20⇒x=100[km]
Therefore the distance between A and B is D1+D2 where D1,D2
is the distance each train traveled untill the meeting. So the distance
is
(100)+(100+20)=220[km]
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