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 4 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.
Shivam said:
4 years ago
In question, it was mentioned that the first half of the distance so for first half time can not be 5 hrs. For that reason those who are getting 225 will be wrong. If he will travel at 21 km/h ge will not reach half of the distance in 5 hrs.
(2)
Jayanth S N said:
1 decade ago
@all its easy guys.....
w.k.t Average speed=Total distance/total time
and also we know
Average speed=2(s1)(s2)/(s1+s2);
s1=24kmph
s2=21kmph
substitute you get avg speed=22.4
w.k.t total time =10hr
therefore total distance =224
w.k.t Average speed=Total distance/total time
and also we know
Average speed=2(s1)(s2)/(s1+s2);
s1=24kmph
s2=21kmph
substitute you get avg speed=22.4
w.k.t total time =10hr
therefore total distance =224
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.
Madivarma said:
8 years ago
This is very simple. Just look at the speeds.take the average of 21 and 24. It comes to 22.5kmph.
Then distance = time x speed.
10 x 22.5 = 225km.
Then see the options. Which is very closer to 225km. 22 km that's it.
Then distance = time x speed.
10 x 22.5 = 225km.
Then see the options. Which is very closer to 225km. 22 km that's it.
Ramana said:
1 decade ago
We know that when dist traveled is equal the its harmonic mean so,
we can get by => avg speed*time= dist.
= 2(21*24)/21+24.
= 1008/45 = 22.4KM/hr.
Avg speed = 22.4km/hr.
Distance = Speed* time = 22.4*10 = 224 km.
we can get by => avg speed*time= dist.
= 2(21*24)/21+24.
= 1008/45 = 22.4KM/hr.
Avg speed = 22.4km/hr.
Distance = Speed* time = 22.4*10 = 224 km.
GETE BASU CHAKMA said:
7 years ago
Let the total distance = X km.
The time is taken by first half journey =(X/2) * 21 hr.
The time is taken by Second half journey =(X/2) * 24 hr.
So, the total time(10 hr) =(X/2) * 21 + (X/2) * 24.
Then we get X= 224 km.
The time is taken by first half journey =(X/2) * 21 hr.
The time is taken by Second half journey =(X/2) * 24 hr.
So, the total time(10 hr) =(X/2) * 21 + (X/2) * 24.
Then we get X= 224 km.
Rati said:
2 decades ago
I am not getting the answer. If we use another method by finding avg. of speed
ie. 21+24=45/2=22.5x10=225
& even we calculate separately
ie. 5x21 = 105
5x24 = 120
Then 105+120=225
I am confused pls explain
ie. 21+24=45/2=22.5x10=225
& even we calculate separately
ie. 5x21 = 105
5x24 = 120
Then 105+120=225
I am confused pls explain
Brijesh said:
1 decade ago
Since total distance is divided in two equal half part.
Therefor 10 can be written as 5+5 = 10.
Time = Distance/Speed (5 = x/2*21 and next 5 = x/2*24).
Place these value.
x/2*21 + x/2*24 = 10.
By solving x = 224.
Therefor 10 can be written as 5+5 = 10.
Time = Distance/Speed (5 = x/2*21 and next 5 = x/2*24).
Place these value.
x/2*21 + x/2*24 = 10.
By solving x = 224.
(1)
Shubham said:
4 years ago
@Naveen.
LCM of 21 and 24 is 168,
168/21 = 7,
168/24 = 8.
But the simple way to solve this question is;
Avrg speed = 2xy/x+y,
2 * 21 * 24/ 21+24,
1008/45 = 22.4.
Distance = speed * time,
= 22.4 *10 =224 km/h.
LCM of 21 and 24 is 168,
168/21 = 7,
168/24 = 8.
But the simple way to solve this question is;
Avrg speed = 2xy/x+y,
2 * 21 * 24/ 21+24,
1008/45 = 22.4.
Distance = speed * time,
= 22.4 *10 =224 km/h.
(6)
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