Aptitude - Time and Distance - Discussion
Discussion Forum : Time and Distance - General Questions (Q.No. 12)
12.
Robert is travelling on his cycle and has calculated to reach point A at 2 P.M. if he travels at 10 kmph, he will reach there at 12 noon if he travels at 15 kmph. At what speed must he travel to reach A at 1 P.M.?
Answer: Option
Explanation:
Let the distance travelled by x km.
| Then, | x | - | x | = 2 |
| 10 | 15 |
3x - 2x = 60
x = 60 km.
| Time taken to travel 60 km at 10 km/hr = |  |
60 |  hrs |
= 6 hrs. |
| 10 |
So, Robert started 6 hours before 2 P.M. i.e., at 8 A.M.
 Required speed = |
|
60 | kmph. |
= 12 kmph. |
| 5 |
Discussion:
93 comments Page 1 of 10.
Arunkumar said:
1 decade ago
How to find that 2. We don't know the starting time. Then how that is calculated.
Xyz said:
1 decade ago
Its 2 hours
12 noon to 2pm = 2 hours
12 noon to 2pm = 2 hours
Das said:
1 decade ago
Hi, could u tell me why we have done 60/5 in last step ?
Ashish said:
1 decade ago
Actually 5 comes as:
Robert start travelling at 8 am. Now difference between 8 am to 1 pm is 5 hrs.
So that 60/5.
Robert start travelling at 8 am. Now difference between 8 am to 1 pm is 5 hrs.
So that 60/5.
Mohamed said:
1 decade ago
This is another way of doing it:
In the last step what you can do instead is (60 / S) - (60 / 15) = 1 following the same logic as the predecessor example while S is the speed that will be arriving @ 1pm.
This will bring us to (900 - 60S) / 15S = 1
-> multiply this two sides to 15S, this will reap 15S = 900 - 60S.
then 75S = 900, S = 12 km/hr.
In the last step what you can do instead is (60 / S) - (60 / 15) = 1 following the same logic as the predecessor example while S is the speed that will be arriving @ 1pm.
This will bring us to (900 - 60S) / 15S = 1
-> multiply this two sides to 15S, this will reap 15S = 900 - 60S.
then 75S = 900, S = 12 km/hr.
Santhosh said:
1 decade ago
How to solve the equation first?
Aamir said:
1 decade ago
We can also solve through avearge speed its easy .x=10,y=15
2xy/x+y
2*10*15/10+15=
300/25=12
2xy/x+y
2*10*15/10+15=
300/25=12
(2)
Vyshu said:
1 decade ago
Why we are subtracting here i.e., x/10-x/15=2;.
And in the next problem why we are adding. Can anyone explain when should add and when should subtract.
And in the next problem why we are adding. Can anyone explain when should add and when should subtract.
(1)
Pardhu said:
1 decade ago
Thank you aamir. Is this applicable for all these type methods. ?
Srinu said:
1 decade ago
Hi vyshu
2 is time between 12noon and 1pm why subtracting
12noon - 2 pm = 2 it is time
x/15-x/10=2 x=60km
12noon time =60/15=4hrs(before) mean 8am
find speed 1pm----------8am to 1pm time is 5 hrs ,distance 60km,speed =? speed=60/5= 12kmph
2 is time between 12noon and 1pm why subtracting
12noon - 2 pm = 2 it is time
x/15-x/10=2 x=60km
12noon time =60/15=4hrs(before) mean 8am
find speed 1pm----------8am to 1pm time is 5 hrs ,distance 60km,speed =? speed=60/5= 12kmph
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