Aptitude - Time and Distance - Discussion
Discussion Forum : Time and Distance - General Questions (Q.No. 9)
9.
A man on tour travels first 160 km at 64 km/hr and the next 160 km at 80 km/hr. The average speed for the first 320 km of the tour is:
Answer: Option
Explanation:
| Total time taken = |  |
160 | + | 160 |  hrs. |
= | 9 | hrs. |
| 64 | 80 | 2 |
 Average speed = |
|
320 x | 2 | km/hr |
= 71.11 km/hr. |
| 9 |
Discussion:
63 comments Page 4 of 7.
Jitender Yaggik said:
8 years ago
@ALL.
Some of my friends are confused in Speed formulas some are using a+b/2 and some are using 2ab/a+b. Now I am going to clear that point, first of all when the distance is same In both then we will use the second formula which is Harmonic mean (2ab/a+b) and when the time is same in both cases then we will use Arithmetic mean a+b/2.
Thank you.
Some of my friends are confused in Speed formulas some are using a+b/2 and some are using 2ab/a+b. Now I am going to clear that point, first of all when the distance is same In both then we will use the second formula which is Harmonic mean (2ab/a+b) and when the time is same in both cases then we will use Arithmetic mean a+b/2.
Thank you.
Shivani said:
8 years ago
Sir, it is asking for 320 km so how can we apply this formula 2xy/ (x+y)?
Ajay said:
8 years ago
Total speed 320km/hr.
64km/h + 80km/hr= 144km/hr.
So the average speed is 144/2= 72 km/hr.
64km/h + 80km/hr= 144km/hr.
So the average speed is 144/2= 72 km/hr.
Prashanthi said:
7 years ago
Thanks for the solution @Kapil.
Arjun said:
7 years ago
Why can't we just take the average of the two numbers and divide by 2, since distance travelled at both the speeds is same.
We get the answer as 72.
We get the answer as 72.
Pronoi said:
7 years ago
Average speed =2 * 64 * 80/64+80.
= 10240/144.
= 71.11 km/hr.
= 10240/144.
= 71.11 km/hr.
Tridib Samanta said:
7 years ago
As the distance of the first half and the second half of the journey is same, i.e. 160 kms.
We can use the formula - [ 2xy / x+y],
=> (2x64x80) / (64+80),
=> 10,240 / 144,
=> 71.1111 km/hr.
Which gives the average speed for the entire journey!
Please note that you could use this formula ONLY IF distances of both halves are SAME.
Here in this problem 160 km each half. So, 320 km total distance of the journey.
All the best!
We can use the formula - [ 2xy / x+y],
=> (2x64x80) / (64+80),
=> 10,240 / 144,
=> 71.1111 km/hr.
Which gives the average speed for the entire journey!
Please note that you could use this formula ONLY IF distances of both halves are SAME.
Here in this problem 160 km each half. So, 320 km total distance of the journey.
All the best!
Priyadharshini G. said:
7 years ago
Given,
Speed 1= 64 km/hr.
Speed 2= 80 km/hr.
Here the distance are same.
Avg. speed = 2 x y /(x+y).
=2 * 64*80/(64+80).
=71.11 km/hr.
Speed 1= 64 km/hr.
Speed 2= 80 km/hr.
Here the distance are same.
Avg. speed = 2 x y /(x+y).
=2 * 64*80/(64+80).
=71.11 km/hr.
Rahul said:
7 years ago
@Sundar.
It's so difficult to cut 10240/144.
It's so difficult to cut 10240/144.
Muklesur said:
7 years ago
2xy/x+y.
2*64*80/64 + 80.
71.111 km/h.
2*64*80/64 + 80.
71.111 km/h.
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