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For how many ordered pairs (x , y) that are solutions of the

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For how many ordered pairs (x , y) that are solutions of the [#permalink] New post 24 May 2007, 05:07
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2x + y = 12
|y| <= 12

For how many ordered pairs (x , y) that are solutions of the system above are x and y both integers?

A. 7
B. 10
C. 12
D. 13
E. 14

OPEN DISCUSSION OF THIS QUESTION IS HERE: for-how-many-ordered-pairs-x-y-that-are-solutions-of-the-110687.html
[Reveal] Spoiler: OA

Last edited by Bunuel on 09 Mar 2014, 22:57, edited 2 times in total.
Renamed the topic, edited the question and added the OA.
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 [#permalink] New post 24 May 2007, 08:28
Can you explain why the Y values go from -12 to 12? I a little new at this forum. I originally got 12 total possibilities.
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 [#permalink] New post 24 May 2007, 09:17
2x + y = 12


|y| <= 12 means that y can be anything between 12 and -12 inclusive. Absolute values always indicates a range of numbers... this is the easy way to think about abs. values.

Ok, now you've narrowed down the answer choices to 25 possible numbers... which doesn't help you with the answers given. Next you need to find a way of eliminating more answer choices...

Simplify 2x + y = 12 to

x + y/2 = 3

Now looking at that, you know y has to be an even number to yield an integer... so the initial pool of 25 numbers is now narrowed down to 13, hence the answer.
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 [#permalink] New post 24 May 2007, 18:57
This is a good question, coz I did not pay attention to the "(x,y) that will yield x and y to be integers" part of the question, so I was stuck with the answer being 25 and was stumped by the choices.
Good job you guys....i guess I should read the question clearly
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Re: PS-ordered pairs (x , y) [#permalink] New post 06 Sep 2011, 23:04
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Balvinder wrote:
2x + y = 12
|y| <= 12


For how many ordered pairs (x , y) that are solutions of the system above are x and y both integers?
A. 7
B. 10
C. 12
D. 13
E. 14


|y| <= 12
-12<=y<=12

2x + y = 12
x=(12-y)/2

To find number of integer pairs, we just need to find even number of y's, because even y will make "(12-y)" even as well and only even numbers divide by 2 evenly to give an integer.

e.g.
x=(12-y)/2; for y=1; x=(12-1)/2=11/2=5.5(Not an integer because y is odd)
x=(12-y)/2; for y=0; x=(12-0)/2=12/2=6(An integer because y is even)

Thus, if we find the number of even y's, we should be good.

-12<=y<=12
What is the first even number greater than or equal to -12?
-12
What is the last even number smaller than or equal to +12?
+12

Count=\frac{Last Even-First Even}{2}+1

Count=\frac{12-(-12)}{2}+1=12+1=13

Ans: "D"
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Re: PS-ordered pairs (x , y) [#permalink] New post 07 Sep 2011, 01:02
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Fluke ,
The approach was awesome
+1
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Re: PS-ordered pairs (x , y) [#permalink] New post 07 Sep 2011, 04:34
Number of ordered pairs = number of integers between 12 and 0 (both inclusive)
= 13
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Re: 2x + y = 12 |y| <= 12 For how many ordered pairs (x [#permalink] New post 09 Mar 2014, 16:11
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Re: For how many ordered pairs (x , y) that are solutions of the [#permalink] New post 09 Mar 2014, 22:58
Expert's post
2x + y = 12
|y| <= 12

For how many ordered pairs (x , y) that are solutions of the system above are x and y both integers?


A. 7
B. 10
C. 12
D. 13
E. 14

Given: -12\leq{y}\leq{12} and 2x+y=12 --> y=12-2x=2(6-x)=even, (as x must be an integer). Now, there are 13 even numbers in the range from -12 to 12, inclusive each of which will give an integer value of x.

Answer: D.

OPEN DISCUSSION OF THIS QUESTION IS HERE: for-how-many-ordered-pairs-x-y-that-are-solutions-of-the-110687.html
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Re: For how many ordered pairs (x , y) that are solutions of the   [#permalink] 09 Mar 2014, 22:58
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