Question

1. A car travels 30 km at a uniform speed of 40 km/hr and the next 30 km at a speed of 20
km/hr. Find its average speed.
​

Answer 1

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$\frac{80}{3}$ Km/hr

step-by-step explanation:

Case 1.

Distance covered = 30 km

Speed of the car = 40 km/hr

Now,

we know that,

Distance = speed × time

=> time = Distance/ speed

therefore,

time taken to cover this distance = 30/40 hr = 3/4 hr.

now,

Case 2.

Distance covered = 30 km

speed of the car = 20 km/hr

=> time taken to cover this Distance = 30/20 hr = 3/2 hr

Now,

we know that,

Average speed = $\frac{Total\:distance\:covered}{Total\:time\:taken}$

Here,

Total distance covered = 30 + 30 = 60 km

and,

Total time taken = 3/4 +3/2 = 9/4 hr

Therefore,

Average speed = 60/(9/4) km/hr

= 60×4/9 km/hr

= 80/3 km/hr