A car travels from A to B at an average speed of 60mph. If the car tak

Question

A car travels from A to B at an average speed of 60mph. If the car takes the exact route on the return trip and has an average speed of 90mph from B to A, what is the average speed for the entire trip?
(A) 65 mph
(B) 72 mph
(C) 75 mph
(D) 80 mph
(E) Cannot be determined.

Archit3110 · Answer

Since route is same so avg speed
2*a*b/(a+b)
2*60*90/150
72 option B

Posted from my mobile device

globaldesi · Answer

Distance is same

so two speeds are along same 
 \frac{2xy}{x+y}

so
its
 \frac{2*90*60}{90+60} 
=72 kmph

B

GMATWhizTeam · Answer

Solution:

Let the distance between point A and B be  x  miles.

From  A  to  B :

Speed  = 60mph . Distance  = x  miles

Time taken  T_1 = \frac{x}{60}  hours.

From  B  to  A :

Speed  = 90mph . Distance  = x  miles

Time taken  T_2 = \frac{x}{90}  hours.

Total distance of the whole journey  = x+x=2x  miles.

Total time of the whole journey  = \frac{x}{60} + \frac{x}{90} = \frac{(3x+2x)}{180} = \frac{5x}{180} = \frac{x}{36}  hours.

Average speed of the whole journey  = \frac{total distance}{total time} = \frac{2x}{x/36}=2	imes 36=72 mph.

Hence the right answer is  Option B .

GynCliff · Answer

Assume the distance from A to B is 180km (always look for a number that is easiest to calculate e.g the LCM of 60 and 90).

Average speed = total distance / total time

Total distance = 180 time 2 = 360km

T1 = distance / speed = 180 / 60 = 3 hrs

T2 = distance /speed = 180 / 90 = 2 hrs

Average speed = 360 / (3 + 2) = 360/5 = (36 * 10 ) / 5 = 36 * 2 = 72km/h

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A car travels from A to B at an average speed of 60mph. If the car tak

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