Eco Wildlife Preserve contains 5x zebras and. . . . .

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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

The OA is the option A.

I don't understand how to solve this DS question. Ay expert could help me? I'd be thankful for your help.

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by Brent@GMATPrepNow » Sat Jan 27, 2018 8:07 am
VJesus12 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

Aside: Here's a video with tips on rephrasing the target question: https://www.gmatprepnow.com/module/gmat- ... cy?id=1100

Answer: A
Brent Hanneson - Creator of GMATPrepNow.com
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