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:
65 comments Page 4 of 7.
Arjun said:
8 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.
Prashanthi said:
8 years ago
Thanks for the solution @Kapil.
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.
Shivani said:
9 years ago
Sir, it is asking for 320 km so how can we apply this formula 2xy/ (x+y)?
Jitender Yaggik said:
9 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.
Swapnil said:
9 years ago
(64+80)/2 = 72.
This answer aprox to 71.11
Therefore the answer is 71.11.
This answer aprox to 71.11
Therefore the answer is 71.11.
Gayathri said:
10 years ago
@Sundar. Your explanations always make me clear, Thanks.
Rahul said:
10 years ago
Why can't we use 64 + 80/2 = 72?
(1)
Roksana1 said:
10 years ago
I'm using solution in this way. Whether it is correct way let me know.
Distance 1 = 160km.
Speed 1 = 64km/hr.
Distance 2 = 160km.
Speed 2 = 80km/hr.
If average distance is 320km.
Then let assume Avg speed = x.
So,
160/64 + 160/80 = 320/x.
20/8 + 16/8 = 320/x (to make the calculation easy let shortleft handed => 20 + 16/8= 320/x numbers).
=> 36/8 = 320/x.
x = 2560/36.
x = 71.11km/hr.
Distance 1 = 160km.
Speed 1 = 64km/hr.
Distance 2 = 160km.
Speed 2 = 80km/hr.
If average distance is 320km.
Then let assume Avg speed = x.
So,
160/64 + 160/80 = 320/x.
20/8 + 16/8 = 320/x (to make the calculation easy let shortleft handed => 20 + 16/8= 320/x numbers).
=> 36/8 = 320/x.
x = 2560/36.
x = 71.11km/hr.
Vengatesh said:
1 decade ago
Super, Thank you all.
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