Time and Distance | Arithmetic aptitude | Discussion Page

What is the average speed of the car over the entire distance ?

I. The car covers the whole distance in four equal stretches at speeds of 10 kmph, 20 kmph, 30 kmph and 60 kmph respectively.

II. The total time taken is 36 minutes.

A) I alone sufficient while II alone not sufficient to answer

B) II alone sufficient while I alone not sufficient to answer

C) Either I or II alone sufficient to answer

D) Both I and II are not sufficient to answer

E) Both I and II are necessary to answer

Option A

Let the whole distance be $4x$ km.

I. Total time taken $=\left(\frac{x}{10}+\frac{x}{20}+\frac{x}{30}+\frac{x}{60}\right)$

$=\frac{(6x+3x+2x+x)}{60}$

$=\frac{12x}{60}$ $=\frac{x}{5}$ .

$\therefore$ Speed $=\frac{Distance}{Time}$ $=\frac{4x}{\left(\frac{x}{5}\right)}$ kmph = 20 km/hr.

$\therefore$ I alone is sufficient to answer the question.

II. alone does not give the answer.

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