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 14 of 15.
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)
Hemansu said:
1 decade ago
Can anyone explain me how did we get 20minutes.
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.
Suchita said:
1 decade ago
These are so much difficult.
Somebody have simple and easy way?
Somebody have simple and easy way?
Asit said:
1 decade ago
We know that the avg speed =2xy/x+y
so 2*21*24/21+24=112/5 km/hr
then distance=speed*time
=>112/5 * 10=224 km.
so 2*21*24/21+24=112/5 km/hr
then distance=speed*time
=>112/5 * 10=224 km.
Sidhila said:
1 decade ago
@abhishek
How did you get 20?
How did you get 20?
Abhishek said:
1 decade ago
(x/21)+(x/24)=20;
taking LCM,we get-
(45x/504)=20;
and 45/504=15/168;
so 15x=168*20;
x=224;
taking LCM,we get-
(45x/504)=20;
and 45/504=15/168;
so 15x=168*20;
x=224;
Neelima said:
2 decades ago
L.C.M of 21, 24 with 3 ans is =3, 7, 8 = multiply you get 168
x/21 + x/24 = 7x + 8x/168 = 20
15x = 20 * 168
x = (20 * 168) / 15
x/21 + x/24 = 7x + 8x/168 = 20
15x = 20 * 168
x = (20 * 168) / 15
Sarika datir said:
2 decades ago
We can calculate it by using formula of avg speed also.
x=21,y=24
Formula of avg spped=2xy/x+y
=2(21*24)/21+24
=1008/45=22.4KM/hr
avg spped=22.4km/hr
distance=Speed* time=22.4*10=224km
x=21,y=24
Formula of avg spped=2xy/x+y
=2(21*24)/21+24
=1008/45=22.4KM/hr
avg spped=22.4km/hr
distance=Speed* time=22.4*10=224km
Amit Kr. Soni said:
2 decades ago
Rati, your method for getting average of speed is wrong,
Because formla of average of speed is = Total distance traveled/Total time taken.
Now let me solve the problem.
Let the total distance = X
& 1st half means X/2
2nd half means also X/2
Again time 4 1st half= X/2*21 =X/42, time 4 2nd half = X/48
According to question: X/42 X/48 = 10hrs.
or, 7x+8x/336=10
or, 15x=3360
So X = 224 Answer.
Because formla of average of speed is = Total distance traveled/Total time taken.
Now let me solve the problem.
Let the total distance = X
& 1st half means X/2
2nd half means also X/2
Again time 4 1st half= X/2*21 =X/42, time 4 2nd half = X/48
According to question: X/42 X/48 = 10hrs.
or, 7x+8x/336=10
or, 15x=3360
So X = 224 Answer.
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