Aptitude - Time and Distance - Discussion
Discussion Forum : Time and Distance - General Questions (Q.No. 8)
8.
The ratio between the speeds of two trains is 7 : 8. If the second train runs 400 km in 4 hours, then the speed of the first train is:
Answer: Option
Explanation:
Let the speed of two trains be 7x and 8x km/hr.
| Then, 8x = |  |
400 |  |
= 100 |
| 4 |
 x = |
|
100 | |
= 12.5 |
| 8 |
Speed of first train = (7 x 12.5) km/hr = 87.5 km/hr.
Discussion:
51 comments Page 3 of 6.
Ganga said:
6 years ago
@Anika.
The speed is 45 kmph.
The speed is 45 kmph.
Soumya said:
7 years ago
s1: s2= 7: 8.
The speed of the second train = distance/time = 400/4 =100.
This 100 corresponds to 8.
7: 8 * 12.5 = 100
Since 7:8 is a ratio, it will get multiplied to the same number only, therefore 7 * 12.5 = 87.5.
The speed of the second train = distance/time = 400/4 =100.
This 100 corresponds to 8.
7: 8 * 12.5 = 100
Since 7:8 is a ratio, it will get multiplied to the same number only, therefore 7 * 12.5 = 87.5.
ASHWANI said:
7 years ago
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.
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.
Nikkyy said:
7 years ago
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.
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.
Bhanu said:
8 years ago
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.
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.
Guru prasad said:
8 years ago
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.
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.
Salman said:
1 decade ago
I don't know why they have provided a confusing method.
Here is a simple method we use the principle of ratios and direct proportion.
7/8 = x/(400/4) (Speeds are directly proportional to their ratio i.e 5.
Speed of x/Speed of y = Ratio of (speed of x/speed of y).
Hence 7/8 = 4x/400 -> x = (400*7)/(8*4) = 878.5 simple as that.
Here is a simple method we use the principle of ratios and direct proportion.
7/8 = x/(400/4) (Speeds are directly proportional to their ratio i.e 5.
Speed of x/Speed of y = Ratio of (speed of x/speed of y).
Hence 7/8 = 4x/400 -> x = (400*7)/(8*4) = 878.5 simple as that.
Prajweetha said:
1 decade ago
Second train runs at 400kms in 4 hours, so in 1 hour its speed is 400/4=100kms/hr.
Let speed of first train be "x".
Ratio is 7:8=x:100.
Then 8x=7*100.
X=700/8.
=87. 5km/hr.
Let speed of first train be "x".
Ratio is 7:8=x:100.
Then 8x=7*100.
X=700/8.
=87. 5km/hr.
Sandeep said:
1 decade ago
Its a ration sum..
then..
Second train runs at 400kms in 4 hours, so in 1 hour its speed is 400/4=100kms/hr.
Now according to ratio concept:-
7:8
means..
total is 15..
then 8/15*x=100
we get,187.5 total speed of both the tain.
now
for first train speed..
7/15*187.5= 87.5 km/hr
then..
Second train runs at 400kms in 4 hours, so in 1 hour its speed is 400/4=100kms/hr.
Now according to ratio concept:-
7:8
means..
total is 15..
then 8/15*x=100
we get,187.5 total speed of both the tain.
now
for first train speed..
7/15*187.5= 87.5 km/hr
Anshu said:
1 decade ago
Speed of the 2nd train =
Total distance it traveled / total time taken
= 400 / 4 = 100kmph
Therefore,
according to the ratio provided,
8x = 100 kmph
x = 12.5 kmph
therefore the the speed of the second train =
7x = 7 (12.5) = 87.5 kmph
I hpoe that is easy.
Total distance it traveled / total time taken
= 400 / 4 = 100kmph
Therefore,
according to the ratio provided,
8x = 100 kmph
x = 12.5 kmph
therefore the the speed of the second train =
7x = 7 (12.5) = 87.5 kmph
I hpoe that is easy.
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