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 3 of 15.
Rakshii said:
3 years ago
First, half of the journey is nothing but 5hr,
So, distance = speed * time.
21*5 = 105.
24*5 = 120.
Total= 225km
So, distance = speed * time.
21*5 = 105.
24*5 = 120.
Total= 225km
(70)
Aleena said:
4 years ago
Let the time taken for the complete first half = x.
Then the time taken for complete second half will be = 10 - x.
Distance = speed * time.
So,
21x = 24(10-x)
21x = 240-24x
21x + 24x=240
45x = 240
x = 240/45
ie 16/3.
Give the value of x to the first equations.
21x=21 * 16/3.
We get 112.
24(10-x) = 24*(10-16/3).
We get 112.
Just add them both to get the total distance.
ie 224.
Then the time taken for complete second half will be = 10 - x.
Distance = speed * time.
So,
21x = 24(10-x)
21x = 240-24x
21x + 24x=240
45x = 240
x = 240/45
ie 16/3.
Give the value of x to the first equations.
21x=21 * 16/3.
We get 112.
24(10-x) = 24*(10-16/3).
We get 112.
Just add them both to get the total distance.
ie 224.
(7)
Matheshg said:
4 years ago
@Sarika Datir.
The formula is used when D is constant.
The formula is used when D is constant.
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)
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)
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)
Santu said:
5 years ago
How come 15? Please explain.
(1)
Charan said:
5 years ago
Let, distance be 'x'
The for the first half, distance = x * 1/2.
For the second half also, distance = x * 1/2.
Then , time = distance/speed.
Therefore, time taken for first half = (x*1/2)/21 = x/42.
Time taken for second half = (x*1/2)24 = x/48.
Therefor total time = x/42 +x/48 and that is given as 10 minutes.
So, x/42+x/48 = 10.
Solving this, you get (48x + 42x) = 48*42*10.
On solving , 90x = 48*42*10.
We get x = 224.
The for the first half, distance = x * 1/2.
For the second half also, distance = x * 1/2.
Then , time = distance/speed.
Therefore, time taken for first half = (x*1/2)/21 = x/42.
Time taken for second half = (x*1/2)24 = x/48.
Therefor total time = x/42 +x/48 and that is given as 10 minutes.
So, x/42+x/48 = 10.
Solving this, you get (48x + 42x) = 48*42*10.
On solving , 90x = 48*42*10.
We get x = 224.
Parkavi said:
5 years ago
Average speed = 2xy/x+y.
Here
X =21.
Y = 24.
Then, the average speed is;
2(21)(24)/45 = 22.4.
Average speed= total distance/total time.
22.4 = X/10,
224 = X,
Finally, the distance is 224.
Here
X =21.
Y = 24.
Then, the average speed is;
2(21)(24)/45 = 22.4.
Average speed= total distance/total time.
22.4 = X/10,
224 = X,
Finally, the distance is 224.
(2)
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)
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