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.
Aman said:
5 years ago
average speed = 2xy/x+y.
So, 2*21*24/21+24.
2*21*24/45,
112/5=22.4.
Distance = time * speed.
= 10*22.4 =>224 kms.
So, 2*21*24/21+24.
2*21*24/45,
112/5=22.4.
Distance = time * speed.
= 10*22.4 =>224 kms.
(1)
Santu said:
5 years ago
How come 15? Please explain.
(1)
Sri Naveen said:
4 years ago
@Amit Kr. Soni.
Anyone please explain to me that how 7x&8x came there?
Anyone please explain to me that how 7x&8x came there?
(1)
Shadab said:
2 decades ago
How this 15x arrives?
Manabendra said:
2 decades ago
Sir, would you please explaine me the 1st line of your explanation?
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
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.
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
Neelima said:
1 decade 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
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;
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