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# The difference between the squares of two positive integers is 2011

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Intern
Joined: 24 Mar 2018
Posts: 8
The difference between the squares of two positive integers is 2011  [#permalink]

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11 Apr 2018, 11:17
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Difficulty:

55% (hard)

Question Stats:

71% (01:49) correct 29% (02:13) wrong based on 82 sessions

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The difference between the squares of two positive integers is 2011 what is the greatest possible sum of those two integers?
A) 1002
B) 1005
C) 1007
D) 1809
E) None of these

source: TIME Mock GMAT
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Joined: 22 Feb 2018
Posts: 190
The difference between the squares of two positive integers is 2011  [#permalink]

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Updated on: 26 Jun 2018, 06:16
1
hetmavani wrote:
The difference between the squares of two positive integers is 2011 what is the greatest possible sum of those two integers?
A) 1002
B) 1005
C) 1007
D) 1809
E) None of these

source: TIME Mock GMAT

Ans : E
Given in the question $$x^2-y^2=2011$$
$$(x+y)(x-y)=2011$$
For maximum possible value of $$(x+y)$$, $$(x-y)$$ should be minimum.
x cannot be equal to y , then minimum value of $$(x-y)$$ is $$1$$.
So it gives Maximum value $$(x+y)=2011$$.

solving $$x-y=1$$ and $$x+y=2011$$, we get $$x=1006, y =1005$$
so using x-y=1,we get value of x and y as integers, which matches the information given in question stem.
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Originally posted by Princ on 11 Apr 2018, 12:08.
Last edited by Princ on 26 Jun 2018, 06:16, edited 1 time in total.
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Location: India
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The difference between the squares of two positive integers is 2011  [#permalink]

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11 Apr 2018, 12:18
1
hetmavani wrote:
The difference between the squares of two positive integers is 2011 what is the greatest possible sum of those two integers?
A) 1002
B) 1005
C) 1007
D) 1809
E) None of these

source: TIME Mock GMAT

The difference between the square of two positive integers is the product
of the sum and difference of the integers. $$x^2 - y^2 = (x + y)(x - y)$$

2011 = 2011*1(when prime-factorized)
Also, neither of the answer options available divide 2011.

Therefore, Option E(None of these) is the only answer possible!
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Joined: 07 Dec 2014
Posts: 1042
Re: The difference between the squares of two positive integers is 2011  [#permalink]

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11 Apr 2018, 14:32
[quote="hetmavani"]The difference between the squares of two positive integers is 2011 what is the greatest possible sum of those two integers?
A) 1002
B) 1005
C) 1007
D) 1809
E) None of these/quote]

(x+y)(x-y)=2011
as 2011 is prime,
x+y=2011
x-y=1
2x=2012
x=1006
subtracting,
2y=2010
y=1005
1006+1005=2011
E
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Re: The difference between the squares of two positive integers is 2011  [#permalink]

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22 Apr 2018, 20:47
X^2-Y^2=(x+y)(x-y)

X+y max means x-y min
So x-yhas to be equal to 1

So x+y=2011

Posted from my mobile device
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Joined: 30 Mar 2017
Posts: 126
GMAT 1: 200 Q1 V1
Re: The difference between the squares of two positive integers is 2011  [#permalink]

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24 Jun 2018, 16:58
pushpitkc wrote:
hetmavani wrote:
The difference between the squares of two positive integers is 2011 what is the greatest possible sum of those two integers?
A) 1002
B) 1005
C) 1007
D) 1809
E) None of these

source: TIME Mock GMAT

The difference between the square of two positive integers is the product
of the sum and difference of the integers. $$x^2 - y^2 = (x + y)(x - y)$$

2011 = 2011*1(when prime-factorized)
Also, neither of the answer options available divide 2011.

Therefore, Option E(None of these) is the only answer possible!

Hi pushpitkc, is there a quick way to determine that 2011 is prime? I'm only aware of the method where we check every prime less than $$\sqrt{2011}$$ but if we do that, the question easily takes 5+ mins.
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Joined: 26 Feb 2016
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Location: India
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Re: The difference between the squares of two positive integers is 2011  [#permalink]

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24 Jun 2018, 22:45
aserghe1 wrote:
pushpitkc wrote:
hetmavani wrote:
The difference between the squares of two positive integers is 2011 what is the greatest possible sum of those two integers?
A) 1002
B) 1005
C) 1007
D) 1809
E) None of these

source: TIME Mock GMAT

The difference between the square of two positive integers is the product
of the sum and difference of the integers. $$x^2 - y^2 = (x + y)(x - y)$$

2011 = 2011*1(when prime-factorized)
Also, neither of the answer options available divide 2011.

Therefore, Option E(None of these) is the only answer possible!

Hi pushpitkc, is there a quick way to determine that 2011 is prime? I'm only aware of the method where we check every prime less than $$\sqrt{2011}$$ but if we do that, the question easily takes 5+ mins.

Hi aserghe1

Unfortunately, that is the shortest method to find whether 2011 is a prime number or not.

However, in this case, we needn't necessarily go to the extent of finding whether it is prime.
We just need to check if the prime numbers in the answer options divide 2011. For instance,
take Option A(1002), which can be prime factorized as 2*3*167. If either of the prime factors
do not divide 2001, we can eliminate that particular option.

Hope this helps you!
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Joined: 30 Mar 2017
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GMAT 1: 200 Q1 V1
Re: The difference between the squares of two positive integers is 2011  [#permalink]

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25 Jun 2018, 15:59
Quote:
Quote:
Hi pushpitkc, is there a quick way to determine that 2011 is prime? I'm only aware of the method where we check every prime less than $$\sqrt{2011}$$ but if we do that, the question easily takes 5+ mins.

Hi aserghe1

Unfortunately, that is the shortest method to find whether 2011 is a prime number or not.

However, in this case, we needn't necessarily go to the extent of finding whether it is prime.
We just need to check if the prime numbers in the answer options divide 2011. For instance,
take Option A(1002), which can be prime factorized as 2*3*167. If either of the prime factors
do not divide 2001, we can eliminate that particular option.

Hope this helps you!

I think you're onto something pushpitkc, but I don't understand the logic behind checking if the prime numbers in the answer options divide 2011. Going with your example, if we take Option A (1002), find its prime factorization (2*3*167)... we see that 2011 is not divisible by 2, so eliminate Option A. How does 2011 not being divisible by 2 allow us to eliminate Option A?
Re: The difference between the squares of two positive integers is 2011 &nbs [#permalink] 25 Jun 2018, 15:59
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