Aptitude - Time and Distance - Discussion

Hello sir, how did come 1/15 at 1st step ?

Hi manasa,


let the speed of the train be x kmph
let the speed of the car be y kmph
it is given that 120km is done by train,so D=120
by the formula D=S*T
T=120/X
and also given the rest is done by the car,
so D=600-120=480 km
T=480/y
then,120/x+480/y=8(read the question given problem clearly,in pbm it is given that to complete 600km journey,it will take 8hrs).
==>1/x+4/y=1/15...............eq1
similarly in case 2:
time for
train=200/x
car=400/y
and also given in pbm 20 min more so,
200/x+400/y=25/3(8hrs+20min=25/3)
==>1/x+2/y=1/24...............eq2
for solving these two equations as mathi said
then u will get 3:4



Hope u understand.
Bye

Please can any one help out this problem.

How they got 8 in first step?

Please can any one tell me how did you get the 1/24 in first step?

Please can any one tell me how did you get the 8 in first step?

Here to solve short cut method....

1/x+4/y=1/15 --> take xy as multiples
(y+4x)/xy=1/15 --> take 15 to left hand side
15y + 60x=xy

Similarly
1/x+2/y=1/24
24y+48x=xy

now easy to equate
15y+60x=24y+48x
60x-48x=24y-15y
12x=9y
x/y=9/12 --> x/y=3/4
hence 3:4

Is there any short method for this?

By doing eqn(1) - eqn(2) we can get:

(4/y)-(2/y) = (1/15)-(1/24)

(4y-2y)/y2=(8-5)/120

2y/y2=3/120

2/y=1/40

y=80

By placing y value in eqn(1) we get x = 60.

Please tell me how did you get the X value?

Hi das 120 (1/x+4/y) = 8 then 1/x+4/y=8/20 that is equal to 1/x+4/y=1/15.