A car travels the first one third of a certain distance with a speed of 20 km hr the next one third ...........

Quant (SSC) Time & distance

A car travels the first one-third of a certain distance with a speed of 20 km/hr, the next one-third distance with a speed of 30 km/hr and the last one-third distance with a speed of 60 km/hr. The average speed of the car for the whole journey is

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Explanation:

Let the total distance covered = LCM of (20, 30, 60) = 60.
As per the question,
Distance covered by the car with each speed = 1/3 x 60 = 20 km
⇒ 20/20 + 20/30 + 20/60 = 60/avg. speed
⇒ 6/3 = 60/avg. speed
⇒ average speed = 30 km/hr.