GMAT Changed on April 16th - Read about the latest changes here

It is currently 26 May 2018, 16:12

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

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

Eco Wildlife Preserve contains 5x zebras and 2x lions

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

Hide Tags

4 KUDOS received
Current Student
User avatar
Joined: 06 Sep 2013
Posts: 1891
Concentration: Finance
GMAT ToolKit User
Eco Wildlife Preserve contains 5x zebras and 2x lions [#permalink]

Show Tags

New post 20 Sep 2013, 15:55
4
This post received
KUDOS
5
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

63% (01:33) correct 37% (01:29) wrong based on 251 sessions

HideShow timer Statistics

Eco Wildlife Preserve contains 5x zebras and 2x lions, where x is a positive integer. If the lions succeed in killing z of the zebras, is the new ratio of zebras to lions less than 2 to 1 ?

(1 ) z > x
(2 ) z = 4
Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 45455
Re: Eco Wildlife Preserve contains 5x zebras and 2x lions [#permalink]

Show Tags

New post 20 Sep 2013, 16:01
Eco Wildlife Preserve contains 5x zebras and 2x lions, where x is a positive integer. If the lions succeed in killing z of the zebras, is the new ratio of zebras to lions less than 2 to 1 ?

The question asks: is \(\frac{5x-z}{2x}<\frac{2}{1}\)? --> is \(x<z\)?

(1 ) z > x. Sufficient.

(2 ) z = 4. Not sufficient.

Answer: A.
_________________

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?
Extra-hard Quant Tests with Brilliant Analytics

Senior Manager
Senior Manager
avatar
Joined: 02 Dec 2014
Posts: 355
Location: Russian Federation
Concentration: General Management, Economics
GMAT 1: 640 Q44 V33
WE: Sales (Telecommunications)
Re: Eco Wildlife Preserve contains 5x zebras and 2x lions [#permalink]

Show Tags

New post 11 Feb 2016, 12:16
jlgdr wrote:
Eco Wildlife Preserve contains 5x zebras and 2x lions, where x is a positive integer. If the lions succeed in killing z of the zebras, is the new ratio of zebras to lions less than 2 to 1 ?

(1 ) z > x
(2 ) z = 4

I did by picking numbers. In option 1 the equation (5x-z)/2x is always less than 2 no matter what values of x and z you pick. In option 2 we only have one value and this is not sufficient
_________________

"Are you gangsters?" - "No we are Russians!"

Expert Post
Math Revolution GMAT Instructor
User avatar
D
Joined: 16 Aug 2015
Posts: 5452
GMAT 1: 800 Q59 V59
GPA: 3.82
Re: Eco Wildlife Preserve contains 5x zebras and 2x lions [#permalink]

Show Tags

New post 12 Feb 2016, 05:48
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.

Eco Wildlife Preserve contains 5x zebras and 2x lions, where x is a positive integer. If the lions succeed in killing z of the zebras, is the new ratio of zebras to lions less than 2 to 1 ?

(1 ) z > x
(2 ) z = 4


When you modify the original condition and the question, they become (5x-z):2x<2:1?, (5x-z)/2x<2?, 5x-z<4x?, x<z?. Therefore, the answer is A.


-> Once we modify the original condition and the question according to the variable approach method 1, we can solve approximately 30% of DS questions.
_________________

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 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Director
Director
User avatar
B
Joined: 04 Jun 2016
Posts: 611
GMAT 1: 750 Q49 V43
COMBINATION OF RATIO AND INEQUALITY [#permalink]

Show Tags

New post 09 Jun 2016, 12:36
Hello a quick query for resolution.
here is a DS question :-

A forest has 5x zebras and 2x lions
Lions kill z number of the zebras, is the new ratio of zebras to lions less than 2 to 1 ?
(1) z > x
(2) z = 4

MY approach
ORIGINAL RATIO =
# of zebras : # of lions = 5x : 2x
Now am I wrong in cancelling x from both num. and denom. at this stage?
Should I keep the expression (5x : 2x) and work with x or should I cancel out x and simplify work forward with (5 : 2)

my next step is
NEW RATIO =
# of surviving zebras : # of lions

5x-z : 2x < 2: 1

or

5-z : 2 < 2: 1

AND THEN SOLVE STATEMENTS A AND B

Thanks in advance
_________________

Posting an answer without an explanation is "GOD COMPLEX". The world doesn't need any more gods. Please explain you answers properly.
FINAL GOODBYE :- 17th SEPTEMBER 2016. .. 16 March 2017 - I am back but for all purposes please consider me semi-retired.

Expert Post
1 KUDOS received
Math Expert
User avatar
V
Joined: 02 Aug 2009
Posts: 5783
Re: COMBINATION OF RATIO AND INEQUALITY [#permalink]

Show Tags

New post 09 Jun 2016, 20:27
1
This post received
KUDOS
Expert's post
LogicGuru1 wrote:
Hello a quick query for resolution.
here is a DS question :-

A forest has 5x zebras and 2x lions
Lions kill z number of the zebras, is the new ratio of zebras to lions less than 2 to 1 ?
(1) z > x
(2) z = 4

MY approach
ORIGINAL RATIO =
# of zebras : # of lions = 5x : 2x
Now am I wrong in cancelling x from both num. and denom. at this stage?
Should I keep the expression (5x : 2x) and work with x or should I cancel out x and simplify work forward with (5 : 2)

my next step is
NEW RATIO =
# of surviving zebras : # of lions

5x-z : 2x < 2: 1

or

5-z : 2 < 2: 1

AND THEN SOLVE STATEMENTS A AND B

Thanks in advance



Hi,

ratio is correct if you are dealing only in ratios of various things but not when you have some numeric value...
this Q has number z, so you will have to work on 5x, because z are going out of 5x and not 5..
so\(\frac{5x-z}{2x}< \frac{2}{1}......5x-z<4x.........x<z\)
so we are looking for is x<z..
statement I gives you that info so suff....
_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html


GMAT online Tutor

1 KUDOS received
Senior Manager
Senior Manager
User avatar
Joined: 18 Jan 2010
Posts: 254
Re: Eco Wildlife Preserve contains 5x zebras and 2x lions [#permalink]

Show Tags

New post 09 Jun 2016, 22:34
1
This post received
KUDOS
jlgdr wrote:
Eco Wildlife Preserve contains 5x zebras and 2x lions, where x is a positive integer. If the lions succeed in killing z of the zebras, is the new ratio of zebras to lions less than 2 to 1 ?

(1 ) z > x
(2 ) z = 4



Once Lions kill zebras.

\(\frac{Zebras}{Lions}\) = \(\frac{5x-z}{2x}\)

If \(\frac{5x-z}{2x}\) < \(\frac{2}{1}\)

Then (since x and z have to be positive values, we can cross multiply)

5x-z < 4x

x < z --> We will check options if this condition is satisfied

We find that Statement 1 is sufficient.

Statement 2 is not sufficient because it dies not say anything about x.

A is the answer.
Expert Post
Top Contributor
1 KUDOS received
SVP
SVP
User avatar
P
Joined: 12 Sep 2015
Posts: 2477
Location: Canada
Re: Eco Wildlife Preserve contains 5x zebras and 2x lions [#permalink]

Show Tags

New post 27 Jan 2018, 09:08
1
This post received
KUDOS
Expert's post
Top Contributor
jlgdr wrote:
Eco Wildlife Preserve contains 5x zebras and 2x lions, where x is a positive integer. If the lions succeed in killing z of the zebras, is the new ratio of zebras to lions less than 2 to 1 ?

(1 ) z > x
(2 ) z = 4


Given: Eco Wildlife Preserve contains 5x zebras and 2x lions, where x is a positive integer. The lions kill z of the zebras

Target question: Is the new ratio of zebras to lions less than 2 to 1 ?

This is the perfect candidate for rephrasing the target question.

ASIDE: If we take the time to rephrase the question in a simpler form, then we can save a ton of time evaluating the statements.

The NEW population of zebras is 5x - z

So, we can ask "Is (5x - z)/2x < 2/1?"

Not bad, but we can go much further than this!.

Since 2x is POSITIVE, we can safely take (5x - z)/2x < 2/1 and multiply both sides by 2x.
When we do this, we get: 5x - z < 4x
Subtract 4x from both sides: x - z < 0
Add z to both sides: x < z

So, we can write....
REPHRASED target question: Is x < z?

Now onto the statements....

Statement 1: z > x
Perfect!!
The answer to the REPHRASED target question is YES, x < z!
Since we can answer the REPHRASED target question with certainty, statement 1 is SUFFICIENT

Statement 2: z = 4
Given this information, there is no way to conclude whether x < z
Since we cannot answer the REPHRASED target question with certainty, statement 2 is NOT SUFFICIENT

Answer: A

RELATED VIDEO

_________________

Brent Hanneson – Founder of gmatprepnow.com

Image

Director
Director
User avatar
S
Joined: 08 Jun 2015
Posts: 504
Location: India
GMAT 1: 640 Q48 V29
Premium Member CAT Tests
Re: Eco Wildlife Preserve contains 5x zebras and 2x lions [#permalink]

Show Tags

New post 19 Apr 2018, 07:21
+1 for option A.

We can re-phrase this question as - (5x-z)/(2x)<2 --> Solving we get x<z. Now hunt for an option that satisfies this equation.

St 1 - Sufficient
St 2- NS

Hence option A.
_________________

" The few , the fearless "

Re: Eco Wildlife Preserve contains 5x zebras and 2x lions   [#permalink] 19 Apr 2018, 07:21
Display posts from previous: Sort by

Eco Wildlife Preserve contains 5x zebras and 2x lions

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


GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

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

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.