GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 20 Aug 2019, 16:26

Close

GMAT 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

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

David and Stacey are riding bicycles on a flat road at a constant rate

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Find Similar Topics 
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 57155
David and Stacey are riding bicycles on a flat road at a constant rate  [#permalink]

Show Tags

New post 28 Feb 2016, 09:40
1
12
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

74% (01:17) correct 26% (01:33) wrong based on 182 sessions

HideShow timer Statistics

David and Stacey are riding bicycles on a flat road at a constant rate. If Stacey is now three miles ahead of David, in how many minutes will Stacey be just two miles ahead of David?

(1) Stacey is traveling at rate of 10 mph and David is traveling at a rate of 12 mph.
(2) 45 minutes ago Stacey was 4.5 miles ahead of David.

_________________
Manager
Manager
avatar
G
Joined: 04 Apr 2015
Posts: 104
Re: David and Stacey are riding bicycles on a flat road at a constant rate  [#permalink]

Show Tags

New post 02 Mar 2016, 10:55
IMO D

In option A the difference in speed is 2(i.e 12-10= 2 mph). So every hour david is gaining 2 mile.
Since we have to maintain a distance of two miles between David and Stacey(presently three), the 1 mile will be covered by David in half n hour(as david is gaining 2 mile /hr,so to gain 1 mile it will take David 1/2 hr and the dist will be 2mile b/w david and stacey).==> Suff

In option B

45 mins ago the dist was 4.5 mile and now dist is 3 mile. Therefore david covered 1.5(4.5-3) mile in 45 min so speed of david catching stacey is 2mph.
By same logic as for opton A==> Suff

SO D
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 7740
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: David and Stacey are riding bicycles on a flat road at a constant rate  [#permalink]

Show Tags

New post 02 Mar 2016, 23:11
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

David and Stacey are riding bicycles on a flat road at a constant rate. If Stacey is now three miles ahead of David, in how many minutes will Stacey be just two miles ahead of David?

(1) Stacey is traveling at rate of 10 mph and David is traveling at a rate of 12 mph.
(2) 45 minutes ago Stacey was 4.5 miles ahead of David.


In the original condition, there are 2 variables(you need to figure out the speed of David and Stacey as you can figure out the time when they are 1 mile apart by knowing their speed). In order to match with the number of equations, you need 2 equations. For 1) 1 equation, for 2) 1 equation, which is likely to make C the answer.
When 1) & 2), for 1), they are 2 miles apart at 1 hour. So, to be 1 mile apart, 30 minutes should pass, which is sufficient.
For 2), 45 minutes:1.5 miles=x;1 mile, x=30 minutes is derived, which is unique and sufficient.
Since 1) = 2), the answer is D.


 For cases where we need 2 more equations, such as original conditions with “2 variables”, or “3 variables and 1 equation”, or “4 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 70% chance that C is the answer, while E has 25% chance. These two are the majority. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer using 1) and 2) separately according to DS definition (It saves us time). Obviously there may be cases where the answer is A, B, D or E.
_________________
MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $79 for 1 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"
Veritas Prep GMAT Instructor
User avatar
D
Joined: 16 Oct 2010
Posts: 9541
Location: Pune, India
David and Stacey are riding bicycles on a flat road at a constant rate  [#permalink]

Show Tags

New post 02 Mar 2016, 23:43
Bunuel wrote:
David and Stacey are riding bicycles on a flat road at a constant rate. If Stacey is now three miles ahead of David, in how many minutes will Stacey be just two miles ahead of David?

(1) Stacey is traveling at rate of 10 mph and David is traveling at a rate of 12 mph.
(2) 45 minutes ago Stacey was 4.5 miles ahead of David.


Distance between Stacey and David = 3 miles
Required distance between them = 2 miles
David needs to cover 1 mile. Time required to do this will depend only on the relative speed of David.

(1) Stacey is traveling at rate of 10 mph and David is traveling at a rate of 12 mph.

David's speed relative to Stacey in 12 - 10 = 2 mph.
Time taken to cover 1 mile relative distance = 1/2 = 0.5 hrs = 30 mins
Sufficient.

(2) 45 minutes ago Stacey was 4.5 miles ahead of David.
In 45 mins (0.75 hrs), David covered 1.5 miles of relative distance.
So his speed relative to Stacey is 1.5/0.75 = 2 mph (same as given in statement 1)
Sufficient.

Answer (D)
_________________
Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >
Intern
Intern
avatar
B
Joined: 01 Jan 2019
Posts: 12
Re: David and Stacey are riding bicycles on a flat road at a constant rate  [#permalink]

Show Tags

New post 26 Jul 2019, 04:14
On what basis is it assumed that David was moving 45 mins ago?

The question also states David and Stacy are riding... nothing about if they both were riding in the past say 45 mins ago.

Couldn't it be the case that Stacy had a head start and David only started to ride say 30 mins ago...
In that case (Sd-Ss)*30 = 4.5...
so Sd-Ss will be different... thus not sufficient

What am i missing? Please help me out here. Thanks :)
GMAT Club Bot
Re: David and Stacey are riding bicycles on a flat road at a constant rate   [#permalink] 26 Jul 2019, 04:14
Display posts from previous: Sort by

David and Stacey are riding bicycles on a flat road at a constant rate

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  





Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne