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 10 of 15.
Sukumar Satyen said:
1 decade ago
Following is explanation:
Total Travel Time = 10 hours.
Let's assume Total Distance = d kms and 1st half (i.e d/2) was completed in x hours at speed of 21 kmph.
=> d/2 = 21x.
=> d/42 = x.....equation (1).
=> 2nd half (i.e d/2) was completed in (10-x) hours @ speed of 24 kmph.
=> d/2 = 24*(10-x).
=> d/48 = 10-x.
=> x = 10-(d/48)....equation (2).
From equation (1) and (2),
=> d/42 = 10-(d/48).
=> d/42 + d/48 = 10.
=> d = 2*5*2*3*7*8/(3*5).
=> d = 224 kms.
Total Travel Time = 10 hours.
Let's assume Total Distance = d kms and 1st half (i.e d/2) was completed in x hours at speed of 21 kmph.
=> d/2 = 21x.
=> d/42 = x.....equation (1).
=> 2nd half (i.e d/2) was completed in (10-x) hours @ speed of 24 kmph.
=> d/2 = 24*(10-x).
=> d/48 = 10-x.
=> x = 10-(d/48)....equation (2).
From equation (1) and (2),
=> d/42 = 10-(d/48).
=> d/42 + d/48 = 10.
=> d = 2*5*2*3*7*8/(3*5).
=> d = 224 kms.
Brijesh said:
1 decade ago
Since total distance is divided in two equal half part.
Therefor 10 can be written as 5+5 = 10.
Time = Distance/Speed (5 = x/2*21 and next 5 = x/2*24).
Place these value.
x/2*21 + x/2*24 = 10.
By solving x = 224.
Therefor 10 can be written as 5+5 = 10.
Time = Distance/Speed (5 = x/2*21 and next 5 = x/2*24).
Place these value.
x/2*21 + x/2*24 = 10.
By solving x = 224.
(1)
Damodhar said:
1 decade ago
Average speed = (2*21*24)/(21+24) = 102/5.
Distance = (102*10)/5 = 224.
Distance = (102*10)/5 = 224.
MALLIKARJUN said:
1 decade ago
Simple trick.
Find average speed because they are given half and half journey.
2xy/x+y......> 2(21)(24)/(21+24).
So average speed = 2(21)(24)/45.
Therefore D = S*T.
= [2(21)(24)/45]*10 = 224.
Find average speed because they are given half and half journey.
2xy/x+y......> 2(21)(24)/(21+24).
So average speed = 2(21)(24)/45.
Therefore D = S*T.
= [2(21)(24)/45]*10 = 224.
Velu said:
1 decade ago
There said half the journey. So why didn't we get half the time for calculation.
Like (5*24)+(5*21) = 225.
Like (5*24)+(5*21) = 225.
Gayu said:
1 decade ago
I can't understand this problem. Please explain.
Ab rahuman said:
1 decade ago
Use average speed formula 2xy/x+y and multiply with time.
Since Distance = Time*Speed.
Since Distance = Time*Speed.
Sajan said:
1 decade ago
Simple formula is 2t(s1*s2)/s1+s2.
So, 2*10(21*24)/21+24.
= 20*504/45.
= 20*11.2.
= 224.
So, 2*10(21*24)/21+24.
= 20*504/45.
= 20*11.2.
= 224.
Ranjitha said:
1 decade ago
How you get 20?
Kavitha said:
1 decade ago
How you got LCM as 45x/105?
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