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
Ordered pairs
This topic has expert replies
My attempt was as follows, I took all values of y starting from 12and -12 (largest absolute given), and placed those values for which x was an integer.
x y
0 12
12 -12
1 10
11 -10
2 8
10 -8
3 6
9 -6
4 4
8 -4
5 2
7 -2
6 0
I realized there was a pattern which was following, so I din make the whole table, just realized it would be 13.....
but here , I have made the whole table...
Lets hope the answer is 13 !
x y
0 12
12 -12
1 10
11 -10
2 8
10 -8
3 6
9 -6
4 4
8 -4
5 2
7 -2
6 0
I realized there was a pattern which was following, so I din make the whole table, just realized it would be 13.....
but here , I have made the whole table...
Lets hope the answer is 13 !
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I would approach like this..
-12 <= y <= 12
For x to be an integer, Y must be even.
So out of 25 values of y, only 13 are even ( -12,-10 ......., 0 , 2, 4 , .... 10,12)
So there are 13 possible pairs that both x and y are integers.
-12 <= y <= 12
For x to be an integer, Y must be even.
So out of 25 values of y, only 13 are even ( -12,-10 ......., 0 , 2, 4 , .... 10,12)
So there are 13 possible pairs that both x and y are integers.
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Nice solution.Mani_mba wrote:I would approach like this..
-12 <= y <= 12
For x to be an integer, Y must be even.
So out of 25 values of y, only 13 are even ( -12,-10 ......., 0 , 2, 4 , .... 10,12)
So there are 13 possible pairs that both x and y are integers.
Very real to GMAT type question.
Regards,
Farooq Farooqui.
London. UK
It is your Attitude, not your Aptitude, that determines your Altitude.
Farooq Farooqui.
London. UK
It is your Attitude, not your Aptitude, that determines your Altitude.
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Really good approach
Mani_mba wrote:I would approach like this..
-12 <= y <= 12
For x to be an integer, Y must be even.
So out of 25 values of y, only 13 are even ( -12,-10 ......., 0 , 2, 4 , .... 10,12)
So there are 13 possible pairs that both x and y are integers.
2x+y = 12, or x = 6- y/2, that implies, even y will give integer x
mody<=12, or 12<=y<=12, or y ranges from -12,-10,-8,.....0,............12
its an AP, -12+(n-1)2 = 12, that implies, n = 13 and hence 13 pairs.
mody<=12, or 12<=y<=12, or y ranges from -12,-10,-8,.....0,............12
its an AP, -12+(n-1)2 = 12, that implies, n = 13 and hence 13 pairs.