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Tavi drives 113 miles at 50 miles per hour and returns via the same route at 60 miles per hour.

Quantity A

Quantity B

Tavi's average speed for the entire round trip

55 mph

A) Quantity A is greater. B) Quantity B is greater. C) The two quantities are equal. D) The relationship cannot be determined from the information given.

Re: Tavi drives 113 miles at 50 miles per hour and returns [#permalink]
21 Oct 2017, 07:11

Here is the trick, the average speed is not computed as a usual average, which would have lead to a wrong answer (C).

It is computed as \(\bar{speed} = \frac{distance_1+distance_2}{time_1+time_2}\). In our case, the distances are equal since the trip is one way and the other, i.e. 113 + 113 = 226 miles, while the time spent is computed as 113/50 = 2.6 hours and 113/60 = 1.883 hours. Substituting in the formula the average speed is 50.41.

Re: Tavi drives 113 miles at 50 miles per hour and returns [#permalink]
13 Mar 2018, 15:49

correct: B route = 113 miles (50 miles / hour) 113/50 hours return_route = 113 miles (60 miles /hour) 113 / 60 hours his average speed is: total miles passed / total time passed = (113 + 113)/ (113/50 + 113/60) = 226 * 300/ 1243 = 54.4 average_speed = 54.4 miles per hour so B is bigger than A

greprepclubot

Re: Tavi drives 113 miles at 50 miles per hour and returns
[#permalink]
13 Mar 2018, 15:49