A car completes a journey in 10 minutes. For the first half of the distance the speed was 60km/h and for the second half the speed was 40km/h. How far is the journey?

TIme travelled = 10 minutes
Distance travelled = x
Speed 1  = 60kmph = 1km per minute
Speed 2 = 40kmph   = 2/3 km per minute
x/2 covered @ 1 km per minute and x/2 covered at 2/3 km per minute
Time taken thus is
(x/2)/1 + (x/2)/(2/3) = 10
x/2 + (x/2)(3/2) = 10
x/2 + 3x/4  = 10
5x/4 = 10
x = (4/5)10 = 8

Thus distance is 8 km
Proof:
4km @ 1 km per minute takes 4 minutes
4km @ 2/3 km per minute takes 6 minutes
Thus total of 10 minutes
  • 1
Total time = 10 minute ,
Distance = x ,
Half of journey = x/2 ,
60 kmph = 1 kmpm (kilometre per minute) ,
40 kmph = 2/3 kmpm ,
A.T.Q ,
( x / 2) / 1 + ( x / 2 ) / 2 / 3 = x / 2 + 3x / 2 =
5x / 4 = 10 min , = x = 4 / 5 * 10 = 8 km.
  • 0
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