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# Paul drives from his apartment to his parents’ house and back. On the

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Math Expert
Joined: 02 Sep 2009
Posts: 56257
Paul drives from his apartment to his parents’ house and back. On the  [#permalink]

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08 Feb 2019, 03:47
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Difficulty:

25% (medium)

Question Stats:

72% (01:58) correct 28% (01:14) wrong based on 72 sessions

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Paul drives from his apartment to his parents’ house and back. On the trip to his parents’ house, he travels at an average speed of 60 miles per hour. On the return trip, Paul drives at an average speed of 80 miles per hour. Which of the following is the closest approximation of Paul’s average speed, in miles per hour, for the round trip?

A. 60.0
B. 68.6
C. 70.0
D. 71.4
E. 80.0

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Paul drives from his apartment to his parents’ house and back. On the  [#permalink]

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08 Feb 2019, 04:22
Bunuel wrote:
Paul drives from his apartment to his parents’ house and back. On the trip to his parents’ house, he travels at an average speed of 60 miles per hour. On the return trip, Paul drives at an average speed of 80 miles per hour. Which of the following is the closest approximation of Paul’s average speed, in miles per hour, for the round trip?

A. 60.0
B. 68.6
C. 70.0
D. 71.4
E. 80.0

Average Speed = Total Distance / Total Time $$= (D+D)/(\frac{D}{60})+(\frac{D}{80})= \frac{2D*240}{7D} = 68.6$$

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Paul drives from his apartment to his parents’ house and back. On the  [#permalink]

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08 Feb 2019, 06:30
3
Bunuel wrote:
Paul drives from his apartment to his parents’ house and back. On the trip to his parents’ house, he travels at an average speed of 60 miles per hour. On the return trip, Paul drives at an average speed of 80 miles per hour. Which of the following is the closest approximation of Paul’s average speed, in miles per hour, for the round trip?

A. 60.0
B. 68.6
C. 70.0
D. 71.4
E. 80.0

distance at both instances is same so

avg speed = 2 * a* b/( a+b)
so 2 * 60* 80 / 140
= ~ 68.6 IMO B
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Re: Paul drives from his apartment to his parents’ house and back. On the  [#permalink]

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19 Jun 2019, 18:41
1
Bunuel wrote:
Paul drives from his apartment to his parents’ house and back. On the trip to his parents’ house, he travels at an average speed of 60 miles per hour. On the return trip, Paul drives at an average speed of 80 miles per hour. Which of the following is the closest approximation of Paul’s average speed, in miles per hour, for the round trip?

A. 60.0
B. 68.6
C. 70.0
D. 71.4
E. 80.0

We can let the one-way distance be 240 miles. Therefore, the average speed of the round trip is:

(240 + 240)/(240/60 + 240/80)

480/(4 + 3)

480/7 ≈ 68.6 mph

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Re: Paul drives from his apartment to his parents’ house and back. On the   [#permalink] 19 Jun 2019, 18:41
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