Is |x| + |y| = 0? : Data Sufficiency (DS)

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02 May 2011, 19:30

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(1)
-2 + 2|-1| = 0

-2 + 2|1| = 0

0 + |0| = 0

(2)

-2 + 2|-1| = 0

-2 + 2|1| = 0

0 + |0| = 0

(1) and (2) are insufficient

(1) and (2) together:

|0| + |0| = 0

So the expression can be 0 only when x and y are 0, if both x and y are negative/positive, |x| + |y| > 0. I wonder how the OA is D.

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Warlock007

Is |x| + |y| = 0
1)x + 2|y| = 0
2)y + 2|x| = 0

I know its an easy one
even i got answer in seconds but still need more perfection in fundamentals of mod questions
m looking forward to a basic fundamental explanation of the same

I think c).
all the above are in absolute value. from question stem we see that for a sum of absolute value to be 0, both the terms should be equal to zero. even if one of the terms is not equal to zero, the sum will nto be equal to zero.

statement 1 says: x + (positive no) = 0 i.e. either both zero or x = -(2y)
statement 2 says: y +(pos no) = 0 again either both zero or y = -(2x)

unless it is mentioed that x and y are positive, id say C. becuase it then becomes clear that x & y have to be zero and so |x| + |y| = 0.

have i missed something?

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05 May 2011, 12:49

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Concepts tested is absolute value

It can not be D the OA. It is most probably C

Obviously on 1) and 2) we can plug -2 and 1 and 0 and 0 for x and y and get a Yes and No answer. Insuff

However on 1+2) we get x + 4 /x/ = 0 so x is negative and -4 x = -x so x =0 and therefore y is equal to 0. Suff

Answer is C

Hope this is helpful

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05 May 2011, 18:47

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Warlock007

Is |x| + |y| = 0
1)x + 2|y| = 0
2)y + 2|x| = 0

I know its an easy one
even i got answer in seconds but still need more perfection in fundamentals of mod questions
m looking forward to a basic fundamental explanation of the same

This is how you can reason it out theoretically:

Question: Is |x| + |y| = 0 ?
A mod is either positive or 0. It can never take a negative value. If sum of two mods is 0, they both individually have to be 0 to give a sum 0. So question comes down to: Is x = y = 0?

1)x + 2|y| = 0
Again, |y| will be either 0 or positive. So x will be 0 in first case (when y = 0) and negative in the second case (when |y| is positive) to give a sum of 0. Hence we cannot say whether x = y = 0. Not sufficient.

2)y + 2|x| = 0
Same is the case here. There is not reason why analysis of this equation should be any different from statement 1 since x and y are just interchanged.

Together, either x = y=0 else x and y both are negative. If x and y both are negative, then x = -2|y| and y = -2|x| i.e. in absolute value terms, x is twice of y and y is twice of x which is not possible. Hence, the only way both statements will hold is if x = y = 0. Hence answer (C).

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21 Jun 2012, 21:54

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nades09

Is |x| + |y| = 0?

1. x + 2|y| = 0
2. y + 2|x| = 0

Thanks

Hi,

|x|+|y|=0?
or |x|=-|y|?
Both |x| and |y| are positive, so is it possible that |x| is negative of some positive quantity,
thus, only possibility would be |x|=|y|=0? and that's the question.

Using (1),
|y|=-x/2
or $x \leq 0$, so, it is possible that x = -1, y = 1/2, then $|x|+|y| \neq 0$
or x =0, y = 0, then $|x|+|y| = 0$, Insufficient.

Using (2);
|x|=-y/2
or $y \leq 0$, so, it is possible that y = -1, x = 1/2, then $|x|+|y| \neq 0$
or y = 0, x = 0, then $|x|+|y| = 0$, Insufficient.

Combining both,
$x \leq 0$, then |x|=-y/2
implies, -x=-y/2 or 2x = y.......(a)

Similarly, $y \leq 0$, then |y|=-x/2
implies, -y=-x/2 or x = 2y........(b)
From (a) & (b)
4y=y, thus y=0 & x=0
Also, $|x|+|y| = 0$. Sufficient.

Answer is (C).

Regards,

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24 Jun 2012, 13:38

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nades09

Is |x| + |y| = 0?

(1) x + 2|y| = 0
(2) y + 2|x| = 0

(1) Not sufficient, but implies that x is not positive.
(2) Again, not sufficient, but implies y is not positive.

When considering (1) and (2) together, we can add the two equations side-by-side and obtain x + 2|y| + y + 2|x| = 0,
and (x + |x|) + |x| + (y + |y|) +|y| = 0 + |x| + 0 + |y| = |x| + |y| = 0.
We used the fact that if x is not positive (it is negative or 0), then x + |x| = 0.

Correct answer - C.

Bunuel

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04 Jul 2013, 01:24

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Bumping for review and further discussion*. Get a kudos point for an alternative solution!

*New project from GMAT Club!!! Check HERE

Theory on Abolute Values: math-absolute-value-modulus-86462.html

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PS Abolute Values Questions to practice: search.php?search_id=tag&tag_id=58

Hard set on Abolute Values: inequality-and-absolute-value-questions-from-my-collection-86939.html

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04 Jul 2013, 04:58

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nades09

Is |x| + |y| = 0?

(1) x + 2|y| = 0
(2) y + 2|x| = 0

Since the Question stem is asking if sum of 2 absolute values (which are positive) equal to 0. We know that sum of 2 positive nos can be zero if both are zero. Hence Question asks if x=y=0

from St1 we have x+2|y|=0
Now if y is less than equal to 0 than we have x-2y=0 or x=2y or x=0 if y is 0
If y>0 then x=-2y

Since using 1 we have more than 1 possible option therefore
A,D ruled out

From st 2 we have y+2|x|=0
If x is less than or equal to zero than y-2x=0 or y=2x or if x=0 then y=0
If x>0 then y=-2x

Again more than 1 solution so Option B ruled out

Combining both statement we get

x=2y ,x=-2y, y=2x and y=-2x and x=0, y=0

Since x=0,y=0 is common from both equation we can say say that |x|+|y|=0
Note that x and y have to be 0 to satisfy all above equations.

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04 Jul 2013, 13:02

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Is |x| + |y| = 0?

(1) x + 2|y| = 0

There are two ways we can solve. One is to get the positive and negative cases of y. On the other hand, we can isolate |y| as the question is looking for the value of |y|+|x|

x + 2|y| = 0
2|y| = -x
|y| = -x/2
if |y| = -x/2 then -x/2 must be positive which means x is negative. Of course, x could also be zero meaning we don't know if the absolute value of x and y = 0
INSUFFICIENT

(2) y + 2|x| = 0
This is a similar statement to the above one, except we have the absolute value of x instead of y.
y + 2|x| = 0
2|x| = -y
|x| = -y/2
As with the above statement -y/2 = an absolute value so y must be negative. However, it could also be = to zero.
INSUFFICIENT

So....from 1 and 2 we know that x<=0 and y<=0 which means that:
x + 2|y| = 0
x-2y = 0

y + 2|x| = 0
y - 2x = 0

y-2x=x-2y
3y=3x
y=x=0
SUFFICIENT
(C)

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13 Oct 2013, 03:05

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Bunuel

Is |x| + |y| = 0?

Since absolute value is non-negative the from $|x| + |y| = 0$ we have that the sum of two non-negative values equals to zero, which is only possible if both of them equal to zero. So, the question basically asks whether $x=y=0$

(1) x + 2|y| = 0. It's certainly possible that $x=y=0$ but it's also possible that $x=-2$ and $y=1$. Not sufficient.

Notice that from this statement $|y|=-\frac{x}{2}$, so $-\frac{x}{2}$ equals to a non-negative value ($|y|$), so $-\frac{x}{2}\geq{0}$ --> $x\leq{0}$.

(2) y + 2|x| = 0. It's certainly possible that $x=y=0$ but it's also possible that $y=-2$ and $x=1$. Not sufficient.

Notice that from this statement $|x|=-\frac{y}{2}$, so $-\frac{y}{2}$ equals to a non-negative value ($|x|$), so $-\frac{y}{2}\geq{0}$ --> $y\leq{0}$.

(1)+(2) We have that $x\leq{0}$ and $y\leq{0}$, hence equations from the statements transform to: $x-2y=0$ and $y-2x=0$. Solving gives $x=y=0$. Sufficient.

Answer: C.

Hope it's clear.

P.S. Please read and follow: rules-for-posting-please-read-this-before-posting-133935.html

Hi Bunuel, why do the "equations from the statements transform to: $x-2y=0$ and $y-2x=0$"? Shouldn't it be -x + 2y = 0 and -y +2x = 0? Hope you can help clarify.

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13 Oct 2013, 04:11

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pauc

Bunuel

Is |x| + |y| = 0?

Since absolute value is non-negative the from $|x| + |y| = 0$ we have that the sum of two non-negative values equals to zero, which is only possible if both of them equal to zero. So, the question basically asks whether $x=y=0$

(1) x + 2|y| = 0. It's certainly possible that $x=y=0$ but it's also possible that $x=-2$ and $y=1$. Not sufficient.

Notice that from this statement $|y|=-\frac{x}{2}$, so $-\frac{x}{2}$ equals to a non-negative value ($|y|$), so $-\frac{x}{2}\geq{0}$ --> $x\leq{0}$.

(2) y + 2|x| = 0. It's certainly possible that $x=y=0$ but it's also possible that $y=-2$ and $x=1$. Not sufficient.

Notice that from this statement $|x|=-\frac{y}{2}$, so $-\frac{y}{2}$ equals to a non-negative value ($|x|$), so $-\frac{y}{2}\geq{0}$ --> $y\leq{0}$.

(1)+(2) We have that $x\leq{0}$ and $y\leq{0}$, hence equations from the statements transform to: $x-2y=0$ and $y-2x=0$. Solving gives $x=y=0$. Sufficient.

Answer: C.

Hope it's clear.

P.S. Please read and follow: rules-for-posting-please-read-this-before-posting-133935.html

Hi Bunuel, why do the "equations from the statements transform to: $x-2y=0$ and $y-2x=0$"? Shouldn't it be -x + 2y = 0 and -y +2x = 0? Hope you can help clarify.

We have that $x\leq{0}$ and $y\leq{0}$, thus $|x|=-x$ and $|y|=-y$. Therefore $x + 2|y| = 0$ becomes $x-2y=0$ and $y + 2|x| = 0$ becomes $y-2x=0$.

Hope it's clear.

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12 Dec 2015, 22:21

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Bunuel

Is |x| + |y| = 0?

Since absolute value is non-negative the from $|x| + |y| = 0$ we have that the sum of two non-negative values equals to zero, which is only possible if both of them equal to zero. So, the question basically asks whether $x=y=0$

(1) x + 2|y| = 0. It's certainly possible that $x=y=0$ but it's also possible that $x=-2$ and $y=1$. Not sufficient.

Notice that from this statement $|y|=-\frac{x}{2}$, so $-\frac{x}{2}$ equals to a non-negative value ($|y|$), so $-\frac{x}{2}\geq{0}$ --> $x\leq{0}$.

(2) y + 2|x| = 0. It's certainly possible that $x=y=0$ but it's also possible that $y=-2$ and $x=1$. Not sufficient.

Notice that from this statement $|x|=-\frac{y}{2}$, so $-\frac{y}{2}$ equals to a non-negative value ($|x|$), so $-\frac{y}{2}\geq{0}$ --> $y\leq{0}$.

(1)+(2) We have that $x\leq{0}$ and $y\leq{0}$, hence equations from the statements transform to: $x-2y=0$ and $y-2x=0$. Solving gives $x=y=0$. Sufficient.

Answer: C.

Hope it's clear.

P.S. Please read and follow: rules-for-posting-please-read-this-before-posting-133935.html

Hi Bunuel,

I solved this question in the following way - still got the right answer (not sure if I am right or it was just a fluke). Please provide input.

|x| + |y| = 0, means both value of x&y needs to be known (preferably zero)

Each statement talks about two variables at the same time -Both Insufficient- So either C or E

Now, Statement 1 is in form of y=mx+c (m=-0.5/+0.5 - slope)
& Statement 2 is in form of y=mx+c (m=-2/+2 - slope)

Since any of the possibilities do not overlap each other, these lines will intersect each other at one point - and thus a solution is possible with the help of both the statements.
Thus C

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28 Jul 2016, 11:58

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Warlock007

Is |x| + |y| = 0
1)x + 2|y| = 0
2)y + 2|x| = 0

I know its an easy one
even i got answer in seconds but still need more perfection in fundamentals of mod questions
m looking forward to a basic fundamental explanation of the same

addition of two positive values will only result in zero if both the numbers are 0. niether 1 nor 2 sufficiently states that.
But if we combine both of them, we have x=y=0 , the only case which satisfies the equations.
hence C. The OA is wrong!

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29 Jul 2016, 01:16

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only when x and y both =0 this will be true

1)may possibilities including one with 0+ 0

2)many possibilities including one with 0+0

1+2,

commn is x=y=0

so C

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Hi Bunuel,

Thank you for your explanation. I am still struggling with the combination of the two statements

(1)+(2) We have that x≤0x≤0 and y≤0y≤0, hence equations from the statements transform to: x−2y=0x−2y=0 and y−2x=0y−2x=0. Solving gives x=y=0x=y=0. Sufficient.

Why do you say the equations transform to x - 2y =0 from x + 2|y| = 0, how can we remove the mod?

Thanks

Bunuel

Is |x| + |y| = 0?

Since absolute value is non-negative the from $|x| + |y| = 0$ we have that the sum of two non-negative values equals to zero, which is only possible if both of them equal to zero. So, the question basically asks whether $x=y=0$

(1) x + 2|y| = 0. It's certainly possible that $x=y=0$ but it's also possible that $x=-2$ and $y=1$. Not sufficient.

Notice that from this statement $|y|=-\frac{x}{2}$, so $-\frac{x}{2}$ equals to a non-negative value ($|y|$), so $-\frac{x}{2}\geq{0}$ --> $x\leq{0}$.

(2) y + 2|x| = 0. It's certainly possible that $x=y=0$ but it's also possible that $y=-2$ and $x=1$. Not sufficient.

Notice that from this statement $|x|=-\frac{y}{2}$, so $-\frac{y}{2}$ equals to a non-negative value ($|x|$), so $-\frac{y}{2}\geq{0}$ --> $y\leq{0}$.

(1)+(2) We have that $x\leq{0}$ and $y\leq{0}$, hence equations from the statements transform to: $x-2y=0$ and $y-2x=0$. Solving gives $x=y=0$. Sufficient.

Answer: C.

Hope it's clear.

P.S. Please read and follow: https://gmatclub.com/forum/rules-for-pos ... 33935.html

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