Aptitude - Time and Distance - Discussion
Discussion Forum : Time and Distance - General Questions (Q.No. 13)
13.
It takes eight hours for a 600 km journey, if 120 km is done by train and the rest by car. It takes 20 minutes more, if 200 km is done by train and the rest by car. The ratio of the speed of the train to that of the cars is:
Answer: Option
Explanation:
Let the speed of the train be x km/hr and that of the car be y km/hr.
| Then, | 120 | + | 480 | = 8  |
1 | + | 4 | = | 1 | ....(i) |
| x | y | x | y | 15 |
| And, | 200 | + | 400 | = | 25 | |
1 | + | 2 | = | 1 | ....(ii) |
| x | y | 3 | x | y | 24 |
Solving (i) and (ii), we get: x = 60 and y = 80.
Ratio of speeds = 60 : 80 = 3 : 4.
Discussion:
84 comments Page 6 of 9.
ID.PRASAD said:
8 years ago
@Liton Das.
200/x +400/y = 25/3,
Now, 200 common.
200 (1/x+2/y) = 25/3.
(1/x+2/y) = (25/3) * (1/200),
After the cancellation,
We get,
(1/x+2/y) = 1/24,
Got it.
200/x +400/y = 25/3,
Now, 200 common.
200 (1/x+2/y) = 25/3.
(1/x+2/y) = (25/3) * (1/200),
After the cancellation,
We get,
(1/x+2/y) = 1/24,
Got it.
Dhirendra mehta said:
8 years ago
How comes 3?
Chandu Balaji said:
8 years ago
Can we use alligation method here. Please clarify my doubt?
Siddhant ojha said:
8 years ago
The solution given is not right because of 8+2/3=26/3 not 25/3.
Rahul Singh said:
8 years ago
Train covers 80Km more and car covers 80Km less, as a result 20min more is required. Suppose train covers 240Km(i.e. 3*80) more and car covers 240km(i.e. 3*80) less than it tooks 60min(i.e. 3*20) more.
Similarly, if train covers 480km more and car covers 480km less than time will increase by 120min i.e. 2hr. It means it the whole journey is covered by train only than it takes 10 hrs(8+2) to complete it. so speed of train = 600/10 = 60km/hr.
Now, time taken by train = 120/60 = 2 hrs.
So, time taken by car = 8 - 2 = 6 hrs.
And, speed of car = 480/6 = 80km/hr.
Speed of train : speed of car = 60:80 = 3:4.
Similarly, if train covers 480km more and car covers 480km less than time will increase by 120min i.e. 2hr. It means it the whole journey is covered by train only than it takes 10 hrs(8+2) to complete it. so speed of train = 600/10 = 60km/hr.
Now, time taken by train = 120/60 = 2 hrs.
So, time taken by car = 8 - 2 = 6 hrs.
And, speed of car = 480/6 = 80km/hr.
Speed of train : speed of car = 60:80 = 3:4.
(4)
Monika said:
8 years ago
Thanks @Ophi.
D.Rajkumar said:
7 years ago
The second one takes 20 minute more then time is 8:20 but 25/3 is 8.3.
So, 33/4 is 8.2 is correct
So, 33/4 is 8.2 is correct
Anjali said:
7 years ago
Thanks @Rahul Singh.
P Chandini said:
7 years ago
If the ratio is known 3:4. How can we find the speed?
Yoonie said:
7 years ago
@D.Rajkumar.
Actually when we say 8.2, the 0.2 there is out of 1 unit or 2 out of 10 or 2 out of 100. There are however 60 minutes in 1 hour which means the same concept cannot be applied since we are calculating out of 60 and not 100. 25/3 is absolutely correct.
Actually when we say 8.2, the 0.2 there is out of 1 unit or 2 out of 10 or 2 out of 100. There are however 60 minutes in 1 hour which means the same concept cannot be applied since we are calculating out of 60 and not 100. 25/3 is absolutely correct.
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