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Al and Barb shared the driving on a certain trip.

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Al and Barb shared the driving on a certain trip.  [#permalink]

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New post 20 Sep 2013, 16:21
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C
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E

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Al and Barb shared the driving on a certain trip. What fraction of the total distance did Al drive?

(1) Al drove for 3/4 as much time as Barb did.
(2) Al's average driving speed for the entire trip was 4/5 of Barb's average driving speed for the trip.
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Re: Al and Barb shared the driving on a certain trip.  [#permalink]

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New post 20 Sep 2013, 18:09
1
Al and Barb shared the driving on a certain trip. What fraction of the total distance did Al drive?

(1) Al drove for 3/4 as much time as Barb did. We don't know their average speeds. Not sufficient.

(2) Al's average driving speed for the entire trip was 4/5 of Barb's average driving speed for the trip. We don;t know the times. Not sufficient.

(1)+(2) When combined we have all we need:

Barb's time = t hours, Al's time = 3/4*t hours.
Barb's speed = r miles per hour and Al's rate = 4/5*r miles per hour.

Barb's distance = rt and Al's distance = 3/5*rt --> Al's covered (3/5*rt)/(rt+3/5*rt)=3/8 of the total distance. Sufficient.

Answer: C.
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Re: Al and Barb shared the driving on a certain trip.  [#permalink]

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New post 02 Apr 2016, 09:16
the way i did it is as follows:

1) r x t = d . I was a little confused about the wording "Al drove for 3/4 as much time as Bard did" sounded to me like I needed to add 3/4 to 1. Meaning 4/4 + 3/4 = 7/4 was the answer I got initially as Al's time. But i agree that the correct way to read the stmt is as 3/4 = Al's time. in my formula r x t = d=> r x 3/4t => i don't know what % of the distance the 3/4t covers, i also don't know the rate at which Al is going, plus i don't know how it relates to Barb, i need more information to make this stmt suffice => insufficient.

2) r x t = d => 4/5r x t => Similar to stmt1, I need more information. insufficient.

Combined. for Al we have the rate and the time => 4/5r x 3/4t = 3/5rt. this formula is in direct comparison to Barbs's => r x t = rt => 3/5 rt + rt =8/5rt => Al's distance over the total distance is => 3/5rt / 8/5rt => 3/8 of the distance. Sufficient! Al drove 3/5th as much as Barb did, meaning that he drove 3/8 of the trip.
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Al and Barb shared the driving on a certain trip.  [#permalink]

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New post 30 Jun 2018, 08:23
Bunuel wrote:
Al and Barb shared the driving on a certain trip. What fraction of the total distance did Al drive?

(1) Al drove for 3/4 as much time as Barb did. We don't know their average speeds. Not sufficient.

(2) Al's average driving speed for the entire trip was 4/5 of Barb's average driving speed for the trip. We don;t know the times. Not sufficient.

(1)+(2) When combined we have all we need:

Barb's time = t hours, Al's time = 3/4*t hours.
Barb's speed = r miles per hour and Al's rate = 4/5*r miles per hour.

Barb's distance = rt and Al's distance = 3/5*rt --> Al's covered (3/5*rt)/(rt+3/5*rt)=3/8 of the total distance. Sufficient.

Answer: C.


Hi Bunuel
Great explanation.
I had a doubt that since we know that time is proportional to distance if the time taken by Al is 3/4 of the time of B, can't we infer from here that the ratio of there distances is 3/4 and Al drove 3/7 of the total distance??????

Thanks in advance
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Re: Al and Barb shared the driving on a certain trip.  [#permalink]

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New post 30 Jun 2018, 10:41
1
suramya26 wrote:
Bunuel wrote:
Al and Barb shared the driving on a certain trip. What fraction of the total distance did Al drive?

(1) Al drove for 3/4 as much time as Barb did. We don't know their average speeds. Not sufficient.

(2) Al's average driving speed for the entire trip was 4/5 of Barb's average driving speed for the trip. We don;t know the times. Not sufficient.

(1)+(2) When combined we have all we need:

Barb's time = t hours, Al's time = 3/4*t hours.
Barb's speed = r miles per hour and Al's rate = 4/5*r miles per hour.

Barb's distance = rt and Al's distance = 3/5*rt --> Al's covered (3/5*rt)/(rt+3/5*rt)=3/8 of the total distance. Sufficient.

Answer: C.


Hi Bunuel
Great explanation.
I had a doubt that since we know that time is proportional to distance if the time taken by Al is 3/4 of the time of B, can't we infer from here that the ratio of there distances is 3/4 and Al drove 3/7 of the total distance??????

Thanks in advance


No. Say you drive twice as fast as I do. Can we say that you cover twice as much distance as I do? No, because we don't how long each of us drives. If you drive for 1 hour and I drive for 100 hours, what fraction of the total distance drive?
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
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Re: Al and Barb shared the driving on a certain trip. &nbs [#permalink] 30 Jun 2018, 10:41
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