Time, Speed & Distance
Aptitude

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Q.

A car travels first half distance between two places with a speed of 40 km/hr and rest of the half distance with a speed of 60 km/hr. The average speed of the car is:

 A.

48 km/hr

 B.

37 km/hr

 C.

44 km/hr

 D.

45 km/hr

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Solution:
Option(A) is correct

Let, the total distance covered be $S$ km.

Total time taken,

$=\dfrac{S/2}{40}+\dfrac{S/2}{60}$

$=\dfrac{S}{2\times 40}+\dfrac{S}{2\times 60}$

$=\dfrac{5S}{240}$

Average speed,

$=\dfrac{S}{\left(\frac{5S}{240}\right)}$

$=S\times \dfrac{240}{5S}$

$= \textbf{48 km/hr}$

Edit: For a quick formula based alternative solution, check comment by Vejayanantham TR.


(3) Comment(s)


Vatsan
 ()

The above formula can be applied, only if the distance travelled is the same.



Vejayanantham TR
 ()

$\dfrac{2xy}{x+y}$

$\dfrac{2*40*60}{40+60} = 48$



Suhail Ahmed
 ()

$=\left( \dfrac{2\times S1\times S2 }{(\frac{S2}{S1})}\right)$