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Let speed be 4v, so 3/4th is 3v
The difference 10 mins(35 mins - 25mins), is the difference in time travelling 24 km at 4v and 3v speed.

(24/3v) - (24/4v) = 10/60 (in hours)
solving we get v = 12, so speed of train 4v = 48 km/hr
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Blackbox
A train after traveling for 50km meets with an accident and then proceeds at 3/4 of its former speed and arrives at its destination 35 minutes late . Had the accident occurred 24 km farther, it would have reached the destination only 25 minutes late. What is the speed of the train.

a) 45
b) 33
c) 48
d) 55
e) 61

Difference of 10min is due to the train travelling 24km at its original speed;

If t be the original time taken to cover 24km at original speed;
then, 4/3t is the time taken at 3/4th speed;
so difference in time taken = 4/3t-t=t/3
t/3= 10/60
or t = 1/2 hrs
so it takes the train 1/2 hr to cross 24km at original speed; so speed of train = 48km / hr
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Blackbox
A train after traveling for 50km meets with an accident and then proceeds at 3/4 of its former speed and arrives at its destination 35 minutes late . Had the accident occurred 24 km farther, it would have reached the destination only 25 minutes late. What is the speed of the train.

a) 45
b) 33
c) 48
d) 55
e) 61

here is less mathematical approach.

let the two end points between which this train is running be A and B. Also suppose that accident occurs at C which is at a distance of 50km from A. thus we have

A---------50km----------C----------------------------B 1)

Time taken to travel the distance after the accident i.e. CB is 35 minutes more than the usual time.

now, if the accident were to occur at 24 km farther, then train would have reached only 25 minutes late. i.e.

A--------50 km----------C---------24--------D---------------B 2)

if we look at the situation depicted in 1) and 2) we will see that 10 minute difference in time is occurring because of this 24 Km. which is traveled by its usual speed (=x) in the later case. thus we have

\(\frac{24*4}{3x}\) - \(\frac{24}{x}\) = \(\frac{10}{60}\)
\(\frac{32}{x}\) - \(\frac{24}{x}\) = \(\frac{1}{6}\)
solving this we get x= 48km/h
Thank you for this.

I am misappropriating something due to which I took longer than usual to solve the problem.

I took the difference of the speed as x/4 (x - 3x/4) and the time to cover this relative speed was 10 min (1/6) and hence by D = S * T, 24 = x/4 * 1/6, which gave me. x = 96 * 6

I tried to use the concept of relative speed that I learnt in other solutions, but I am doing something incorrectly.

Can someone please help with identifying the mistake and perhaps content to hone the relative speed concept?
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glagad
manpreetsingh86
Blackbox
A train after traveling for 50km meets with an accident and then proceeds at 3/4 of its former speed and arrives at its destination 35 minutes late . Had the accident occurred 24 km farther, it would have reached the destination only 25 minutes late. What is the speed of the train.

a) 45
b) 33
c) 48
d) 55
e) 61

here is less mathematical approach.

let the two end points between which this train is running be A and B. Also suppose that accident occurs at C which is at a distance of 50km from A. thus we have

A---------50km----------C----------------------------B 1)

Time taken to travel the distance after the accident i.e. CB is 35 minutes more than the usual time.

now, if the accident were to occur at 24 km farther, then train would have reached only 25 minutes late. i.e.

A--------50 km----------C---------24--------D---------------B 2)

if we look at the situation depicted in 1) and 2) we will see that 10 minute difference in time is occurring because of this 24 Km. which is traveled by its usual speed (=x) in the later case. thus we have

\(\frac{24*4}{3x}\) - \(\frac{24}{x}\) = \(\frac{10}{60}\)
\(\frac{32}{x}\) - \(\frac{24}{x}\) = \(\frac{1}{6}\)
solving this we get x= 48km/h
Thank you for this.

I am misappropriating something due to which I took longer than usual to solve the problem.

I took the difference of the speed as x/4 (x - 3x/4) and the time to cover this relative speed was 10 min (1/6) and hence by D = S * T, 24 = x/4 * 1/6, which gave me. x = 96 * 6

I tried to use the concept of relative speed that I learnt in other solutions, but I am doing something incorrectly.

Can someone please help with identifying the mistake and perhaps content to hone the relative speed concept?

Not fully following your approach, but the key idea here is that the train saves 10 minutes, or 1/6 of an hour, by traveling 24 km at the speed of x compared to the speed of 3x/4. The difference in time can be expressed as:

24/x - 24/(3x/4) = 1/6

This shows the time saved due to the change in speed. Solving this equation gives x = 48.

Answer: C.
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Unit is missing :/ I arrived to km per min and get stucked loosing time reviewing what calculation did I do wrong
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take me 3:27s to solve this problem :( a bit long
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