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 4 of 6.
Sai said:
9 years ago
Thank you all for explaining the solution in different ways.
Sri said:
9 years ago
Here is the simple method :
400/8 = 50.
400 - 50 = 350.
350/4 = 87.5.
400/8 = 50.
400 - 50 = 350.
350/4 = 87.5.
Nasir said:
9 years ago
If a person drives from point A to B with the speed of 40 km/hr and returns on the same path with the speed of 80 km/hr. Find the average speed of a person?
Can anyone solve this problem?
Can anyone solve this problem?
Jatin said:
10 years ago
How to solve problem which is given in ratio? Any specific formula for that?
(1)
Raghu said:
10 years ago
400/4 = 100 km/hr.
8/7 = 100/x.
x = 87.5.
8/7 = 100/x.
x = 87.5.
Pratibha said:
1 decade ago
The answer and the method to solve is right but is their ratio is right? NO.
Because 87.5/100 is not equal to 7:8.
87.8/100 = 0.87.
Why? Can anyone answer my question?
Because 87.5/100 is not equal to 7:8.
87.8/100 = 0.87.
Why? Can anyone answer my question?
Arun said:
1 decade ago
Easy way is here.
We know that ratio of two train is = 7:8.
Speed of 1st train = ?
Speed of 2nd train = 400\4 = 100 kmphr.
So, 1st train:2nd train = 7:8.
? : 100.
So divide 100 by 8 we will get = 12.5.
Now multiply 1st train ratio with 12.5.
i.e 12.5*7 = 87.5.
So the speed of first train = 87.5 kmphr.
We know that ratio of two train is = 7:8.
Speed of 1st train = ?
Speed of 2nd train = 400\4 = 100 kmphr.
So, 1st train:2nd train = 7:8.
? : 100.
So divide 100 by 8 we will get = 12.5.
Now multiply 1st train ratio with 12.5.
i.e 12.5*7 = 87.5.
So the speed of first train = 87.5 kmphr.
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.
Awesomeness said:
1 decade ago
This problem was really easy!:).
Ophi said:
1 decade ago
Step 1 :
Find the speed of the Second train.
Runs at 400kms in 4 hours, S=D/T.
400/4 = 100kms/hr.
Step 2 :
Find the speed of first train.
Let speed of first train be "x".
By comparing the Ratio.
7:8 = x:100.
Then 8x = 7*100.
x = 700/8.
= 87.5km/hr.
Find the speed of the Second train.
Runs at 400kms in 4 hours, S=D/T.
400/4 = 100kms/hr.
Step 2 :
Find the speed of first train.
Let speed of first train be "x".
By comparing the Ratio.
7:8 = x:100.
Then 8x = 7*100.
x = 700/8.
= 87.5km/hr.
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