Aptitude - Problems on Trains - Discussion

Its simple .

T = D/S

Therefore total distance = 27x+17y and total speed = x+y

Total time = 23

23= 27x+17y/x+y

@niveditha

Since both train crossing each other in 23s, so have to multiply 23 by sum of speed of both train.

Let, the ist train speed v1=X m/s and T1=27s
2nd trin speed V2=Y m/s and T2=17s
Then S1=V1*T1=27x
S2=V2*T2=17Y

Both are in opposite dir. Then speed is S=S1-S2=27X-17Y

They cross each other means time difference 23(X-Y)=23X-23Y
now...
27X-17Y=23X-23Y
4X=-6Y
X/Y=-3/2=3/2(BECZ speed is not -ve)
X:Y=3:2

If two trains running at the speed x & y respectively in opposit direction then their relative velocity is (x+y) m/s.

Now if two trains cross each other then they have to cross total length of two trains which is (27x+17y).

Now time taken for crssng the total length = (27x+17y)/(x+y) i.e 23.

27            17
      23
23-17=6          27-23=4

Then ratio become 3:2

Hi Lokesh,

Can you please explain why you've said 27x-24x=23y-17y.....?


I can't see figure of 24 ain't where???

Thanks in advance....

Thanks Y.S.Rama Krishna

I understood the answer now. :)

Hi friends in smart way....

To find out the speed ratio so ,

formula is Length = speed*time
so,

speed = length /time

here 2 trains so two different length and speed so the formula

s1+s2=L1+L2/time

speed we don't know so we take X,Y for speed for 2 trains
respectively ....
use above formula:

X+Y=L1+L2/23

HERE
L1=speed*time (speed is not given so take it as X,time is given that is 27)

L2= speed*time (speed is not given so take it as Y,time is given that is 17)
SO L1=27X
L2=17Y
apply it,
X+Y=27X+17Y/23

SO SOLVE IT
23(X+Y)=27X+17Y
23X+23Y=27X+17Y

separate the X and Y terms so we get

23X-27X+23Y-17Y=0

WE GET:
-4X+6Y=0
6Y=4X

RATIO (means difference of X and Y)
SO FRIEND,

X/Y=6/4=3/2
SO THE RATIO IS 3:2

@ chanti
its length=speed*time
so length of first train=27*x mts
and length of 2nd train= 17*y mts

The 1st train sec 27-23=4.

The 2nd train sec 23-17=6.

So both are divide by 2.

4/2=2, and 6/3=3.

So the ratio is 3:2 its right method?