GRE Prep Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Davis drove from Amityville to Beteltown at 50 miles per
[#permalink]
15 Jul 2018, 02:55
15 Jul 2018, 02:55
Expert Reply
9
Bookmarks
00:00
Question Stats:
61% (01:05) correct
38% (01:15) wrong based on 140 sessions
Hide Show timer Statistics
Davis drove from Amityville to Beteltown at 50 miles per hour, and returned by the same route at 60 miles per hour.
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.
Quantity A |
Quantity B |
Davis’s average speed for the round trip, in miles per hour |
\(55\) |
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: Davis drove from Amityville to Beteltown at 50 miles per
[#permalink]
15 Jul 2018, 03:05
15 Jul 2018, 03:05
Expert Reply
1
Bookmarks
Explanation
Never take an average speed by just averaging the two speeds (50 mph and 60 mph). Instead, use the formula Average Speed = Total Distance ÷ Total Time. Fortunately, for Quantitative Comparisons, you can often sidestep actual calculations.
Davis’s average speed can be thought of as an average of the speed he was traveling at every single moment during his journey—for instance, imagine that Davis wrote down the speed he was going during every second he was driving, then he averaged all the seconds. Since Davis spent more time going 50 mph than going 60 mph, the average speed will be closer to 50 than 60, and Quantity B is greater.
If the distances are the same, average speed is always weighted towards the slower speed.
To actually do the math, pick a convenient number for the distance between Amityville and Beteltown —for instance, 300 miles (divisible by both 50 and 60). If the distance is 300 miles, it took Davis 6 hours to drive there at 50 mph, and 5 hours to drive back at 60 mph. Using Average Speed = Total Distance ÷ Total Time (and a total distance of 600 miles, for both parts of the journey), you get the following:
Average Speed =\(\frac{600}{11}\frac{miles}{hours}\)
Average Speed = 54.54 … (which is less than 55)
The result will be the same for any value chosen. Quantity B is greater.
Never take an average speed by just averaging the two speeds (50 mph and 60 mph). Instead, use the formula Average Speed = Total Distance ÷ Total Time. Fortunately, for Quantitative Comparisons, you can often sidestep actual calculations.
Davis’s average speed can be thought of as an average of the speed he was traveling at every single moment during his journey—for instance, imagine that Davis wrote down the speed he was going during every second he was driving, then he averaged all the seconds. Since Davis spent more time going 50 mph than going 60 mph, the average speed will be closer to 50 than 60, and Quantity B is greater.
If the distances are the same, average speed is always weighted towards the slower speed.
To actually do the math, pick a convenient number for the distance between Amityville and Beteltown —for instance, 300 miles (divisible by both 50 and 60). If the distance is 300 miles, it took Davis 6 hours to drive there at 50 mph, and 5 hours to drive back at 60 mph. Using Average Speed = Total Distance ÷ Total Time (and a total distance of 600 miles, for both parts of the journey), you get the following:
Average Speed =\(\frac{600}{11}\frac{miles}{hours}\)
Average Speed = 54.54 … (which is less than 55)
The result will be the same for any value chosen. Quantity B is greater.
Re: Davis drove from Amityville to Beteltown at 50 miles per
[#permalink]
05 Aug 2018, 00:18
05 Aug 2018, 00:18
Its good to keep in mind that the average speed will be close to slower speed. hecne B
