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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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chetan2u
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A car travels from A to B at an average speed of 60mph. If the car tak [#permalink] New post   04 Aug 2021, 23:37
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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.
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B
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Re: A car travels from A to B at an average speed of 60mph. If the car tak [#permalink] New post   05 Aug 2021, 00:14
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Since route is same so avg speed
2*a*b/(a+b)
2*60*90/150
72 option B

chetan2u wrote:
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.


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Re: A car travels from A to B at an average speed of 60mph. If the car tak [#permalink] New post   05 Aug 2021, 00:16
Distance is same

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

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

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Re: A car travels from A to B at an average speed of 60mph. If the car tak [#permalink] New post   05 Aug 2021, 00:46
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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 \(= \frac{total distance}{total time} = \frac{2x}{x/36}=2\times 36=72\)mph.

Hence the right answer is Option B.
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Re: A car travels from A to B at an average speed of 60mph. If the car tak [#permalink] New post   25 Oct 2021, 05:46
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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Re: A car travels from A to B at an average speed of 60mph. If the car tak [#permalink] New post   28 Nov 2022, 06:58
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Re: A car travels from A to B at an average speed of 60mph. If the car tak [#permalink]
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