Aptitude - Time and Distance - Discussion

Let Distance is 2D=D for the first halt+D for the second half.

Total time =10hr.
Time taken in first half+Time taken in second half=10hr so,
T1/2 + T/2=10 Now Time = distance/speed.
D/21 + D/24=10.
(D*24 + D*21)/21*24=10 solve it we get.
45x=5040 = D= 112 it is the time taken half journey.
2D=112*2=224km.

I HOPE YOU UNDERSTAND.

We know that speed = distance/time,
let speed be x km/hr.
we are calculating speed for 2nd train,
x=400/4,
x =100,

Give ratio of speeds is 7 and 8.
so taking this,
8----------->100.
7------------> x ?.
x=(7*100)/8,
x=87.5km/hr.

Given speed in ratio : 7:8.
First speed = 7x.
Second speed = 8x.

7x/8x = x(?)/400/4.

7x/8x = x/100.

7x*100 = 8x*x.
700x = 8x*x.

Cancel x in both sides,
700 = 8x.
x = 700/8.
x = 87.5 km/hr.

We know that speed = distance/time.

So, consider speed of 1st train is s1 similarly s2.
Given ratio of their speeds is s1:s2 = 7:8.

Therefore, s1/s2 = (d1/t1) * (t2/d2) -------> (1).

Assume d1 as x, as it covers x km in 1 hour.

Therefore substituting these values in equation (1) we get,
7/8 = (x/1hour) * (4hour/400km).

By cross multiplication we get 87.5km/hr.

We can do it directly,

400/4=100,
(7/8)*100=87.5.

It's easy to solve when we go by options.
In question, they have given details about the second train. Now using formula s=d/t ,we get s=400/4=100.

First train speed is not known, but the ratio of speeds is given in question as 7:8.
We got second trains speed i.e 100,

Now let's look into the options (the options tell about first trains speed ) and when we take the last option 87.5:100 (//speed of first train: speed of the second train ) we get 7:8.Thus concluded that the last option is right.:)

Ratio of train speed = 7:8.
Second train = 400 in 4 hours,
Speed = 100km/h,
8x = 100,
x = 100÷8 = 25/2,
Then, 7x = 25/2 * 7,
=175/2 = 87.5.

@Anika.

The speed is 1927. Is it right?

The odometer of a car reads 57321.0 km when the clock shows time 8.30am. What is the distance moved by a car at 8.50 am, the odometer reading has changed to 57336.0km. Calculate the speed of the car and express the speed in km/hr.

Solve and find the solution.

@Nasir.

I also did not understand how to solve the problem.

Can anyone find the solution for Nasir's question.