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.
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:
8 years ago
Sir, it is asking for 320 km so how can we apply this formula 2xy/ (x+y)?
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.
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:
9 years ago
@Sundar. Your explanations always make me clear, Thanks.
Rahul said:
9 years ago
Why can't we use 64 + 80/2 = 72?
(1)
Roksana1 said:
9 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:
9 years ago
Super, Thank you all.
Laxmi said:
9 years ago
Excellent way of clarifying the doubts.
Damodhar said:
1 decade ago
Average speed = (2*80*64)/(64+80) = 71.11.
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