A car travels the first one third of a certain distance with a speed of 10 km/hr, the next one third with a speed of 20 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

A

18 km/hr

B

24 km/hr

C

30 km/hr

D

36 km/hr

Medium

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Solution

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Correct option is A)

Let the total distance travelled be x km Then total time taken = $10x/3 +20x/3 +60x/3 =30x +60x +180x $ $=1806x+3x+x =18010x =18x $ hrs Then average speed = $=TotaltimetakenTotaldistancetravelled $ $=x/18x $ km/hr = 18 km/hr