in Quantitative Aptitude edited by
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An automobile travels from city $A$ to city $B$ and returns to city $A$ by the same route. The speed of the vehicle during the onward and return journeys were constant at $60km/h$ and $90 km/h$, respectively. What is the average speed in $km/h$ for the entire journey?

  1. $72\hspace{0.2cm} km/h$
  2. $73\hspace{0.2cm} km/h$
  3. $74\hspace{0.2cm} km/h$
  4. $75 \hspace{0.2cm}km/h$
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3 Comments

75km/hr
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@ Lakshman Patel RJIT

Can u plz chk the answer key?

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1

@srestha

right answer is 72km/hr

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1

2 Answers

4 votes
4 votes
Best answer

$\text{Average Speed} = \dfrac{\text{Total Distance travelled}}{\text{Total time taken}}$

Total Distance travelled $=2d$

Total time taken $=$ Time taken from $A$ to $B$ + Time taken from $B$ to $A$

$=\dfrac{d}{60}+\dfrac{d}{90}$

Average speed $=\dfrac{2d}{\dfrac{d}{60}+\dfrac{d}{90}}=\dfrac{2d*180}{5d}=72km/hr$

Hence, option (A) is correct

edited by
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$average speed $$=$$ total \ distance / total\ time$

                       $ = (d + d) / (d/60 + d/90)$

                        $= (2 * 60 *90) / (60 +90)$

                     $   =72 km/hr$
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how total distance 60*90??

that is speed ,na?
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Answer:

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