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:
143 comments Page 7 of 15.
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.
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?
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.
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.
Rubi said:
8 years ago
2*21*24/21*24 = 22.4*10 = 224.
Surender said:
8 years ago
First half hour the speed is 21 so total distance would be 21 * 5 = 105 km,
And in second-hour distance would be 24 * 5 = 120 km,
So, the Total distance be 105 + 120 = 225 km.
Why this is not correct?
And in second-hour distance would be 24 * 5 = 120 km,
So, the Total distance be 105 + 120 = 225 km.
Why this is not correct?
Bappi sah said:
8 years ago
You can also solve it by applying formula 2xy/x+y.
Sharayu Vidhate said:
8 years ago
D = St.
5*21+5*24 = 225km.
5*21+5*24 = 225km.
Soham said:
8 years ago
21+24 = 45,
45/2 = 22.5,
22.5x10 = 225.
45/2 = 22.5,
22.5x10 = 225.
Abhii said:
8 years ago
For first half (x/21).
Second half (x/24).
Is x the total distance or half of the distance.
Question says to find the total journey but here it got x=225 which is the first half distance.
So total should be x+x. 225+225=450.
Second half (x/24).
Is x the total distance or half of the distance.
Question says to find the total journey but here it got x=225 which is the first half distance.
So total should be x+x. 225+225=450.
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