Aptitude - Time and Distance - Discussion

By,
speed 1 (10 kmph) he would reach at point A at 2 P.M.
speed 2 (15 kmph) he would reach at point A at 12 noon.
we know that speed = distance time ^ -1
let the distanc be x
then
x/10 - x/15 = 2
3x - 2x /30 = 2
x/30 = 2
x = 60
the distance is 60 km
@the speed of 10 kmph he would require 10 hours to reach point A.
therefore he left his point of starting 6 hours ago.
time was 14:00 hours - 6 hours = 8 hours. or 8 A.M.
total between 6 a.m. and
08:00 hours - 13:00 hours = 05:00 hours
time = 05:00 hours
distance = 60 km [ we have already found out]
speed = ?
speed = distance time^-1
60 / 5 - 12
therefore, the speed = 12 kmph.

We need to calculate the distance, then we can calculate the time and finally speed .

Lets solve this,

Let the distance travelled by x km.

Time = Distance/Speed.

x10-15 = 2[because, 2 pm - 12 noon = 2 hours] 3x-2x=60 =>x=60.

Time = Distance*Speed,

Time@10km/hr = 60/10 = 6 hours

So 2 P.M. - 6 = 8 A.M

i.e. Robert starts at 8 A.M.


He have to reach at 1 P.M.
i.e,diff between 8 A.M to 1P.M in 5 hours

So, Speed = distance/time => 60/5 = 12 km/hr

x/10-x/15=2
=>3x-2x=60

I didn't get the proper method.

How it comes anyone could tell me briefly it will be helpful for me.

Thank you Raja.

Simple one

2pm-12=2 hour

Similarly 15km-10km=5km

5km/2hour=2.5km/h

initial 10+2.5=12.5 nearer to 12

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

Thank you aamir. Is this applicable for all these type methods. ?

How to solve the equation first?

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.

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.