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# 0 < x < y, and x and y are consecutive integers. If the difference bet

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Senior Manager
Joined: 02 Jan 2017
Posts: 293
0 < x < y, and x and y are consecutive integers. If the difference bet  [#permalink]

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27 Feb 2017, 01:27
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Difficulty:

45% (medium)

Question Stats:

64% (02:03) correct 36% (02:04) wrong based on 175 sessions

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0 < x < y, and x and y are consecutive integers. If the difference between x^2 and y^2 is 12,201, then what is the value of x?

(A) 6,100

(B) 6,101

(C) 12,200

(D) 12,201

(E) 24,402
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Re: 0 < x < y, and x and y are consecutive integers. If the difference bet  [#permalink]

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27 Feb 2017, 21:57
3
3
Hi vikasp99,

This question can be solved in a couple of different ways. It's also built around some specific Number Properties, so if you're not sure how to approach the question, you can take advantage of those patterns and take a great guess.

We're told that X and Y are CONSECUTIVE INTEGERS (0 < X < Y) and that Y^2 - X^2 = 12,201. We're asked for the value of X.

To start, it's interesting that the DIFFERENCE ends in a 1. When subtracting the squares of consecutive integers, there are only a couple of ways that this can occur:

Y ends in a 1 and X ends in a 0
Y ends in a 6 and X ends in a 5

From the answer choices, we can clearly see that it's the first option - and that the correct answer is either Answer A or Answer C. If you're not sure what to do next, then you could guess and move on. However, if you want to continue working, you don't actually have to square two big numbers to find the solution to this question.

Since the two variables are consecutive, we can rewrite Y as (X + 1), so the original equation can be written as...

(X+1)^2 - X^2 = 12,201
X^2 + 2X + 1 - X^2 = 12,201
2X + 1 = 12,201
2X = 12,200
X = 6,100

GMAT assassins aren't born, they're made,
Rich
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##### General Discussion
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Joined: 19 Jan 2017
Posts: 2
Location: India
Re: 0 < x < y, and x and y are consecutive integers. If the difference bet  [#permalink]

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27 Feb 2017, 01:34
1
1

Since x and y are consecutive integers you can take y=x+1.

So y^2-x^2=2x+1=12201
2x=12200
x=6100.

Sent from my Nexus 5 using GMAT Club Forum mobile app
Intern
Joined: 26 Dec 2016
Posts: 28
0 < x < y, and x and y are consecutive integers. If the difference bet  [#permalink]

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Updated on: 20 Mar 2018, 11:34
EMPOWERgmatRichC wrote:
Hi vikasp99,

This question can be solved in a couple of different ways. It's also built around some specific Number Properties, so if you're not sure how to approach the question, you can take advantage of those patterns and take a great guess.

We're told that X and Y are CONSECUTIVE INTEGERS (0 < X < Y) and that Y^2 - X^2 = 12,201. We're asked for the value of X.

To start, it's interesting that the DIFFERENCE ends in a 1. When subtracting the squares of consecutive integers, there are only a couple of ways that this can occur:

Y ends in a 1 and X ends in a 0
Y ends in a 6 and X ends in a 5

From the answer choices, we can clearly see that it's the first option - and that the correct answer is either Answer A or Answer C. If you're not sure what to do next, then you could guess and move on. However, if you want to continue working, you don't actually have to square two big numbers to find the solution to this question.

Since the two variables are consecutive, we can rewrite Y as (X + 1), so the original equation can be written as...

(X+1)^2 - X^2 = 12,201
X^2 + 2X + 1 - X^2 = 12,201
2X + 1 = 12,201
2X = 12,200
X = 6,100

GMAT assassins aren't born, they're made,
Rich

Hi, EMPOWERgmatRichC When I first did the problem, I didn't actually come up with an answer, but did end up with a 61 while trying to figure out an approach. So I figured out that it had to be y^2 - x^2 = 12,201. So, I simplified 12,201 to 12,200 to make it more manageable (without doing the algebra). I then divided 12,200 by 2 which gave me 6,100 (just because I needed to try something). I thought this was a trick or some flaw in my thinking so I actually eliminated that choice. Was I just lucky in getting the 6,100 or is there an avenue to the solution somewhere in that train of thought without realizing the substitution method of y=x+1?

Originally posted by rnz on 20 Mar 2018, 11:30.
Last edited by rnz on 20 Mar 2018, 11:34, edited 1 time in total.
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Re: 0 < x < y, and x and y are consecutive integers. If the difference bet  [#permalink]

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20 Mar 2018, 11:33
arkbatman wrote:

Since x and y are consecutive integers you can take y=x+1.

So y^2-x^2=2x+1=12201
2x=12200
x=6100.

Sent from my Nexus 5 using GMAT Club Forum mobile app

Another way of factoring could be..

y^2 - x^2 = ( y + x ) (y - x)

Since y = x+1

This becomes 2x + 1 = 12201
2x = 12200
x = 6100.

Best,

Posted from my mobile device
_________________
Regards,

“Do. Or do not. There is no try.” - Yoda (The Empire Strikes Back)
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Joined: 01 Nov 2015
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0 < x < y, and x and y are consecutive integers. If the difference bet  [#permalink]

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26 Apr 2018, 04:18
or another way:
(x-y)*(x+y)= 12 201
(x-y) = 12 201 - which is impossible because x-y= -1 (consecutive integers) and x<y
(x+y) = 12 201 - it is possible. Hence we must look at answer choices where C, D, E we can easily eliminate

We have A (6 100) and B (6 101), well it is not a big deal to understand that only A (6 100) suits to our problem.

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Re: 0 < x < y, and x and y are consecutive integers. If the difference bet  [#permalink]

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27 Apr 2018, 09:55
1
vikasp99 wrote:
0 < x < y, and x and y are consecutive integers. If the difference between x^2 and y^2 is 12,201, then what is the value of x?

(A) 6,100

(B) 6,101

(C) 12,200

(D) 12,201

(E) 24,402

Since x and y are consecutive integers, we can let y = x + 1; thus:

(x + 1)^2 - x^2 = 12,201

x^2 + 2x + 1 - x^2 = 12,201

2x + 1 = 12,201

2x = 12,200

x = 6,100

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Re: 0 < x < y, and x and y are consecutive integers. If the difference bet  [#permalink]

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28 Apr 2018, 08:57
Sum of 2 consecutive numbers is always equal to the difference of their Squares.
This is always true.

So in this case sum should be equal to 12,201.
out of the options, all the options are greater than 12,201 except for a,b and c.
and since the numbers are consecutive, the numbers have to be 6,100 and 6,101

Since it is given that x<y, therefore, x=6,100

Ans - A
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Joined: 23 Feb 2015
Posts: 1262
Re: 0 < x < y, and x and y are consecutive integers. If the difference bet  [#permalink]

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02 Sep 2018, 14:30
EMPOWERgmatRichC wrote:
Hi vikasp99,

This question can be solved in a couple of different ways. It's also built around some specific Number Properties, so if you're not sure how to approach the question, you can take advantage of those patterns and take a great guess.

We're told that X and Y are CONSECUTIVE INTEGERS (0 < X < Y) and that Y^2 - X^2 = 12,201. We're asked for the value of X.

To start, it's interesting that the DIFFERENCE ends in a 1. When subtracting the squares of consecutive integers, there are only a couple of ways that this can occur:

Y ends in a 1 and X ends in a 0
Y ends in a 6 and X ends in a 5

From the answer choices, we can clearly see that it's the first option - and that the correct answer is either Answer A or Answer C. If you're not sure what to do next, then you could guess and move on. However, if you want to continue working, you don't actually have to square two big numbers to find the solution to this question.

Since the two variables are consecutive, we can rewrite Y as (X + 1), so the original equation can be written as...

(X+1)^2 - X^2 = 12,201
X^2 + 2X + 1 - X^2 = 12,201
2X + 1 = 12,201
2X = 12,200
X = 6,100

GMAT assassins aren't born, they're made,
Rich

Hi rich, hope u are well. I am very glad to have your explanation-your explanation is always fantastic! May I have another shortcut way, please?
Thanks...
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Re: 0 < x < y, and x and y are consecutive integers. If the difference bet  [#permalink]

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02 Sep 2018, 14:38
ScottTargetTestPrep wrote:
vikasp99 wrote:
0 < x < y, and x and y are consecutive integers. If the difference between x^2 and y^2 is 12,201, then what is the value of x?

(A) 6,100

(B) 6,101

(C) 12,200

(D) 12,201

(E) 24,402

Since x and y are consecutive integers, we can let y = x + 1; thus:

(x + 1)^2 - x^2 = 12,201

x^2 + 2x + 1 - x^2 = 12,201

2x + 1 = 12,201

2x = 12,200

x = 6,100

i'm a bit confused about the bold part above! if x and y are consecutive integers, we can also let x = y + 1, right?
Thanks__
_________________
“The heights by great men reached and kept were not attained in sudden flight but, they while their companions slept, they were toiling upwards in the night.”

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3700 Unique Official GMAT Quant Questions
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Joined: 02 Sep 2009
Posts: 58434
Re: 0 < x < y, and x and y are consecutive integers. If the difference bet  [#permalink]

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02 Sep 2018, 21:19
ScottTargetTestPrep wrote:
vikasp99 wrote:
0 < x < y, and x and y are consecutive integers. If the difference between x^2 and y^2 is 12,201, then what is the value of x?

(A) 6,100

(B) 6,101

(C) 12,200

(D) 12,201

(E) 24,402

Since x and y are consecutive integers, we can let y = x + 1; thus:

(x + 1)^2 - x^2 = 12,201

x^2 + 2x + 1 - x^2 = 12,201

2x + 1 = 12,201

2x = 12,200

x = 6,100

i'm a bit confused about the bold part above! if x and y are consecutive integers, we can also let x = y + 1, right?
Thanks__

Notice that we are also told that 0 < x < y, so y = x + 1.
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Re: 0 < x < y, and x and y are consecutive integers. If the difference bet   [#permalink] 02 Sep 2018, 21:19
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