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Senior Manager Joined: 20 May 2014
Posts: 282
Followers: 18

Kudos [?]: 50 , given: 220

Which is greater: 2x^2-7x-3 5x^2+x-3 [#permalink] 00:00

Question Stats: 78% (00:59) correct 21% (01:19) wrong based on 14 sessions
 Quantity A Quantity B 2x^2-7x-3 5x^2+x-3

A. The quantity in Column A is greater
B. The quantity in Column B is greater
C. The two quantities are equal
D. The relationship cannot be determined from the information given

Kudos for correct solution.
[Reveal] Spoiler: OA Director Joined: 03 Sep 2017
Posts: 521
Followers: 1

Kudos [?]: 344  , given: 66

Re: Which is greater: 2x^2-7x-3 5x^2+x-3 [#permalink]
2
KUDOS
Summing 3, subtracting 2x^2 and summing 7x on both quantities, we get a comparison between 0 and 3x^2+8x = x(3x+8). Then, this expression has two possible solutions, 0 and -8/3. Thus, in one case the two quantities are equal and in the other A is greater.

Manager  Joined: 26 Jun 2017
Posts: 104
Followers: 0

Kudos [?]: 39 , given: 38

Re: Which is greater: 2x^2-7x-3 5x^2+x-3 [#permalink]
IlCreatore wrote:
Summing 3, subtracting 2x^2 and summing 7x on both quantities, we get a comparison between 0 and 3x^2+8x = x(3x+8). Then, this expression has two possible solutions, 0 and -8/3. Thus, in one case the two quantities are equal and in the other A is greater.

thanks for good explaination, I harried to get the roots of the both quantities without thinking
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What you think, you become.

Intern Joined: 11 Jan 2018
Posts: 44
Followers: 0

Kudos [?]: 33 , given: 7

Re: Which is greater: 2x^2-7x-3 5x^2+x-3 [#permalink]
In such questions of quantitative comparison, always first simplify the two quantities as below:

Quantity A: $$2x^2$$ - 7x - 3
Quantity B: $$5x^2$$ + x - 3

First, you can add 3 on both quantities, because it will not change the answer. i.e if a quantity is greater, after addition or subtraction by same number to both quantities, the greater quantity will remain greater. Also if both quantities are equals, the addition and subtraction has no effect, and both will remain equal after adding or subtracting same number to both quantities.

Thus, after adding 3 and 7x to both quantities,

Quantity A: $$2x^2$$
Quantity B: $$5x^2$$ + 8x

Now, similarly, we can subtract $$2x^2$$ from both quantities and get,

Quantity A: 0
Quantity B: $$3x^2$$ + 8x

Now, at this point, again you don't need to plugin. Just you need to think and use common sense here:

$$3x^2$$ is either 0 or positive. If x is 0, which can be possible, then the two quantities becomes equal. Otherwise, if x positive, then Quantity B is greater. And if x is negative, then Quantity A become greater.

Thus, Choice D is correct.
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1 kudos = 1000 Thanks Re: Which is greater: 2x^2-7x-3 5x^2+x-3   [#permalink] 09 Mar 2018, 07:46
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