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# Tom drives to take a GMAT test at an average speed of 50 kilometers pe

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Math Expert
Joined: 02 Sep 2009
Posts: 52390
Tom drives to take a GMAT test at an average speed of 50 kilometers pe  [#permalink]

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07 Oct 2016, 01:40
00:00

Difficulty:

15% (low)

Question Stats:

82% (02:10) correct 18% (02:13) wrong based on 114 sessions

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Tom drives to take a GMAT test at an average speed of 50 kilometers per hour. The moment he arrives at his destination, he realizes that he was confused and that the test would take place on the next day. He immediately returns home the same way, at an average speed of 30 kilometers per hour. If Tom drove 40 kilometers from home to the GMAT test location, how many kilometers per hour is Tom's average speed during his entire journey?

A. 35
B. 37.5
C. 40
D. 42.5
E. 45

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Re: Tom drives to take a GMAT test at an average speed of 50 kilometers pe  [#permalink]

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07 Oct 2016, 04:00
Since the distance for the travel is the same,
the formula for average speed = (2*a*b)/(a+b)

Substituting values a=50,b=30 in the equation,
we get average speed 37.5kmph(Option B)
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Re: Tom drives to take a GMAT test at an average speed of 50 kilometers pe  [#permalink]

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07 Oct 2016, 18:44
Avg. speed = (Distance to GMAT + Distance from GMAT) /( Time to GMAT + Time from GMAT)
Since Tom came back the same way => total distance traveled is 40 x 2 = 80 km

Time to GMAT = 40 / 50 = 4/5
Time from GMAT = 40 / 30 = 4/3

Total time: 4/5 +4/3 = 32/15
Avg. speed = 80 /(32/15) = 75/2 = 37.5 -> option B
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Re: Tom drives to take a GMAT test at an average speed of 50 kilometers pe  [#permalink]

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19 Feb 2017, 23:11
Distance between Tom's home to the GMAT test location is not relevant in calculating the average speed of his journey
formula for average speed = $$\frac{2a*b}{a+b}$$

where a is speed of tom when he goes from his home to gmat test location
and b is speed when tom comes back from gmat test location to his home
average speed =$$\frac{2*50*30}{50+30}$$ = 37.5

Re: Tom drives to take a GMAT test at an average speed of 50 kilometers pe &nbs [#permalink] 19 Feb 2017, 23:11
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