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 6 of 15.
Anshu said:
1 decade ago
Let the equal distance be x
[remember the value of x is the half the total distance]
speed are 21kmph and 24 kmph
we know that speed = distance time^-1
therefore,
time = distance speed^-1
10 = x/21 + x/24
10 = 24x + 21x / 504
5040 = 45x
560 = 5x
112 = x
since the x = 1/2 of the distance
total distance = 2x = 2 (112)= 224kmph
[remember the value of x is the half the total distance]
speed are 21kmph and 24 kmph
we know that speed = distance time^-1
therefore,
time = distance speed^-1
10 = x/21 + x/24
10 = 24x + 21x / 504
5040 = 45x
560 = 5x
112 = x
since the x = 1/2 of the distance
total distance = 2x = 2 (112)= 224kmph
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
Rahul said:
1 decade ago
21*5=105 1st half
24*5=120 2nd half
total 225 approx 224 ans=224
24*5=120 2nd half
total 225 approx 224 ans=224
Abhik said:
1 decade ago
Avg speed = 2xy/x+y = 2.21.24/(21+24)= 112/5
distance= speed * tym = 112/5 * 10 = 224....
distance= speed * tym = 112/5 * 10 = 224....
Lakshmi said:
1 decade ago
Can anyone explain me 2nd step.
Muhammad Umair Kabir said:
1 decade ago
Distance = (Speed x Time).
First five hours speed was 21 km/ h
So D1 = 21 * 5 = 105
Next five hours speed was 24 km / h
D2 = 24 * 5 = 120
ADD them 225 km / h which is nearer to 224 km / h
First five hours speed was 21 km/ h
So D1 = 21 * 5 = 105
Next five hours speed was 24 km / h
D2 = 24 * 5 = 120
ADD them 225 km / h which is nearer to 224 km / h
Syed said:
1 decade ago
To apply formulae 2uv/(u+v),
where,
s = Distance;
u = First Half velocity which is 21kmph
v = Second Half Velocity which is 24kmph
=>(2*21*24)/(21+24)
=>(1008)/45
=>22.4kmph.
Therefore,average speed = 22.4km/hr
s = vt
s = 22.4km/hr x 10hrs
s=224km.
where,
s = Distance;
u = First Half velocity which is 21kmph
v = Second Half Velocity which is 24kmph
=>(2*21*24)/(21+24)
=>(1008)/45
=>22.4kmph.
Therefore,average speed = 22.4km/hr
s = vt
s = 22.4km/hr x 10hrs
s=224km.
Dave said:
1 decade ago
How is @Muhammed way incorrect? that what I did it close but if this was not a multiple choice it would be wrong so can anyone explain it to me. When I mean explain like dumb it right down please.
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.
K Padmanaban said:
1 decade ago
The derived answer is as far as I am concerned is wrong. Because it is clearly stated that half of the journey is @21 kmph and rest is @24 kmph.
We can simply take the average speed as (21+24)/2 = 45/2.
And multiply the speed with the time taken i.e 45/2*10 = 225 km.
It is simple to derive from the distance formula i.e.
Distance = speed * time taken
Got it.
We can simply take the average speed as (21+24)/2 = 45/2.
And multiply the speed with the time taken i.e 45/2*10 = 225 km.
It is simple to derive from the distance formula i.e.
Distance = speed * time taken
Got it.
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