Question
A car travels the first one-third of a certain distance with a speed of 10 km/hr, the next one-third distance with a speed of 20 km/hr , and the last one-third distance with a speed of 60 km/hr . The average of the car for the whole journey is :
Answer: Option A
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Let the whole distance travelled be `x` km and the average of the car for the whole journey be y km/hr.
Then, `((x//3))/(10) +( (x//3))/(20) + ((x //3))/(60) = x/y`
`hArr x/30 + x/60 + x/180 = x/y`
`hArr 1/18 y = 1 hArr y` = 18 km/hr.
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