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 2 of 15.
Jinto said:
1 decade ago
@suchitha
First calculate average speed of 21 and 24 using the formula 2xy/x+y then multiply it with 10 then we will get the answer distance = speed*time easy method.
First calculate average speed of 21 and 24 using the formula 2xy/x+y then multiply it with 10 then we will get the answer distance = speed*time easy method.
Hemansu said:
1 decade ago
Can anyone explain me how did we get 20minutes.
Atul said:
1 decade ago
Question first line: man completes journey in 10 hrs.
In second line: he travels 1/2 of total distance (x) not the time at the rate of 21 km/hr
and 1/2 distance (x) not time at the rate of 25 km/hr.
TIME =DISTANCE/SPEED :1:((DISTANCE=1/2x)/(SPEED=21)for first half
:2:((DISTANCE=1/2x)/(SPEED=25)for second half
TOTAL TIME 10hrs =:1:+:2: =((1/2)x/21)+((1/2)x/24)
In second line: he travels 1/2 of total distance (x) not the time at the rate of 21 km/hr
and 1/2 distance (x) not time at the rate of 25 km/hr.
TIME =DISTANCE/SPEED :1:((DISTANCE=1/2x)/(SPEED=21)for first half
:2:((DISTANCE=1/2x)/(SPEED=25)for second half
TOTAL TIME 10hrs =:1:+:2: =((1/2)x/21)+((1/2)x/24)
Anu said:
1 decade ago
Thanks sarika.
Abhinav said:
1 decade ago
The best way to choose the answer.
Check the option and find the multiple of 21 (divisible by 7) and.
(b) is right because it's a divisble by 7 and also multiple of 21.
Check the option and find the multiple of 21 (divisible by 7) and.
(b) is right because it's a divisble by 7 and also multiple of 21.
Amit said:
1 decade ago
We know that when dist travlled 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.
Shro said:
1 decade ago
Thank you Abhishek :).
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
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