Question: Fractions with Variables

Comment on Fractions with Variables

Can I multiply both sides times x, and the subtract 1?
greenlight-admin's picture

No, we can't do that, because we don't know whether x is positive or negative. For more on this, see the following video: https://www.greenlighttestprep.com/module/gre-quantitative-comparison/vi...

Hi, could you also plug in numbers for this strategy? I used x=1 and still received the same answer (Quantity A is greater) but I'm not sure if this would be a correct way of doing it?

Thanks
greenlight-admin's picture

Plugging in only 1 value is not enough to be absolutely certain of the correct answer. For more on this, see https://www.greenlighttestprep.com/module/gre-quantitative-comparison/vi... (the part about guaranteeing the correct answer starts at 3:00)

For this particular question, plugging in only 1 value worked, but it won't always work.

If I plug in x=-1, I get 0 for A and -2 for B.
When I plug in x=1, I get 2 for A and 0 for B
...hence I got the answer D.
Could you clarify where I went wrong? Thanks.
greenlight-admin's picture

Case 1) x = -1
We get 0 for Quantity A, and we get -2 for Quantity B.
So, Quantity A is greater

Case 2) x = 1
We get 2 for Quantity A, and we get 0 for Quantity B
So, Quantity A is still greater

I hope that helps.

Cheers,
Brent

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