Question
Fri May 25, 2012 By: Anneshwa

a car covers half a distnace in a speed of 40 km/hr nd other half of the distance at a speed of 60km/hr.find the average spped of the car.

Expert Reply
Fri May 25, 2012

The car covers the firsthalf at the v1 speed, of 40 km/h, and the other half at the v2 speed, of 60 km/h.

The first half of distance is covered in the time t1, and the other halfin the time t2.

We'll write the formula of speed:

v = x/t (1)

v1 = (x/2)/t1

We'll substitute v1:

40 = (x/2)/t1

t1 = x/80 hour

v2 = (x/2)/t2

We'll substitute v2:

60 = (x/2)/t2

t2 = x/120 hour

Now, we'll write the average speed:

av. v = total distance covered/total time taken

av. v = x/(t1+t2)

We'll substitute t1 and t2:

av. v = x/(x/80+x/120)

av. v = 80*120/(80+120)

av. v = 9600/200

av. v = 48 Km/h

The average speed of the car is av. v = 48 Km/h.

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