Eco Wildlife Preserve contains 5x zebras and 2x lions

Question

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

Bunuel · Answer

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.

Konstantin1983 · Answer

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

MathRevolution · Answer

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.

LogicGuru1 · Answer

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

chetan2u · Answer

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....

adiagr · Answer

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.

BrentGMATPrepNow · Answer

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
 https://www.youtube.com/watch?v=MyG1K3ee69w

spetznaz · Answer

+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.

hillhuangcp · Answer

why can't we solve for x for statement 2? Since the z value is given, if we plug it in, x will be smaller than 4 right?

Bunuel · Answer

The question ask whether x < z. (2) says z = 4. How can we say from that whether x < 4?

hillhuangcp · Answer

understood. Thanks

Eco Wildlife Preserve contains 5x zebras and 2x lions

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Eco Wildlife Preserve contains 5x zebras and 2x lions

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

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My Rewards