Aptitude - Time and Distance - Discussion
Discussion Forum : Time and Distance - General Questions (Q.No. 7)
7.
A man complete a journey in 10 hours. He travels first half of the journey at the rate of 21 km/hr and second half at the rate of 24 km/hr. Find the total journey in km.
Answer: Option
Explanation:
| (1/2)x | + | (1/2)x | = 10 |
| 21 | 24 |
 |
x | + | x | = 20 |
| 21 | 24 |
15x = 168 x 20
| x = |
 |
168 x 20 |  |
= 224 km. |
| 15 |
Discussion:
141 comments Page 12 of 15.
Manoj said:
8 years ago
Avg.of two speeds = (24+21)/2 = 22.5km/hr.
Time = 10 hr.
Distance = speed*time = 22.5*10 = 225km/hr ~ 224km/hr.
Time = 10 hr.
Distance = speed*time = 22.5*10 = 225km/hr ~ 224km/hr.
Rajat said:
8 years ago
Average Speed={(2XY)/(X+Y)}.
= {(2*21*24)/(21+24))
= 112/5 km/hr.
Distance=Speed*time=(112/5)*10=224 KM.
= {(2*21*24)/(21+24))
= 112/5 km/hr.
Distance=Speed*time=(112/5)*10=224 KM.
Speed said:
8 years ago
d=s*t.
Let the total distance be 2d.
for first part,
distance=d
time taken be=t
speed=21 km/hr.
for the second part
dis=d
time=10-t
speed=24 km/hr
Since distance covered is equal
so,
d for 1st half=d for the 2nd half
t*21=(10-t)*24
Using this I calculated the time for the individual half's through get the distance.
but I am not able to get the correct answer. Can anyone tell me the logic behind that?
Let the total distance be 2d.
for first part,
distance=d
time taken be=t
speed=21 km/hr.
for the second part
dis=d
time=10-t
speed=24 km/hr
Since distance covered is equal
so,
d for 1st half=d for the 2nd half
t*21=(10-t)*24
Using this I calculated the time for the individual half's through get the distance.
but I am not able to get the correct answer. Can anyone tell me the logic behind that?
Anup said:
8 years ago
It's quite simple,
Avg speed is the harmonic mean of those two speeds (as the distances are same)
So, avg speed would be , avg speed = 2*21*24 / (21+24) = 22.4 kmph
Now, time is given as 10 hours.
So, d = s * t
d = 22.4 *10
d = 224 km.
Avg speed is the harmonic mean of those two speeds (as the distances are same)
So, avg speed would be , avg speed = 2*21*24 / (21+24) = 22.4 kmph
Now, time is given as 10 hours.
So, d = s * t
d = 22.4 *10
d = 224 km.
Rajesh said:
8 years ago
Distance =speed*time.
So x=(21*5)+(24*5)=225.
X=225 km.
Why should it not be like this? Please explain.
So x=(21*5)+(24*5)=225.
X=225 km.
Why should it not be like this? Please explain.
Maya said:
8 years ago
For these kind ques, there is a simple formula i.e.
Distance= 2* time* product of speeds / addition of speeds
ans: distance = 2*10*21*24 /21+24.
=10080/45,
= 224 km.
Distance= 2* time* product of speeds / addition of speeds
ans: distance = 2*10*21*24 /21+24.
=10080/45,
= 224 km.
Captain said:
7 years ago
Thank you @Jing.
Yuva said:
7 years ago
Clearly, 10hrs is there, why they taken time is X hrs? please explain me.
Dhaval said:
7 years ago
Hear if total distance is X.
And hear fix first 1/2 at fix speed and another half at other fix speed.
So we can assume avg speed so [ speed (1) + speed (2) ] / 2 so we get avg speed for a total this x.
Then for 10 hr final answer is *10 so we get 225.
And hear fix first 1/2 at fix speed and another half at other fix speed.
So we can assume avg speed so [ speed (1) + speed (2) ] / 2 so we get avg speed for a total this x.
Then for 10 hr final answer is *10 so we get 225.
Sai kumar said:
7 years ago
I didn't understand this, can you explain this question?
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