Is xy < 0? (1) 5|x| + |y| = 0 (2) |x| + 5|y| = 0

That's not correct.

Is xy < 0?

(1) 5|x| + |y| = 0. Since absolute value is always non-negative then we have that the sum of two non-negative values (5|x| and |y|) is zero, which is only possible if each is zero --> x=y=0 --> xy=0. Sufficient.

(2) |x| + 5|y| = 0. The same here. Sufficient.

Answer: D.
_________________

Statement 1 => x = y = 0. Sufficient.
Statement 2 => x = y = 0. Sufficient.

Choice D.

D as well,
but think about it -
(1) 5|x| + |y| = 0
When is a sum equal to zero? one is negative, one is positive. But || (absolute value?, not sure what is the English for it) can't be negative, thus both |x| an |y| should be equal to zero. This means xy clearly is not < 0, but equal to zero. Sufficient
(2) same thing for this option

question is X and y are opposite sign?

stmt 1 : 5x=-y
x/y = - 5, x and y are opposite sign , sufficient.

stmt2L x=-5y, x/y = -5 , x and y are opposite sign , sufficient.


if x and y are same sign x/y will always be positive.

Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

Is xy < 0?


In the original condition, there are 2 variables(x,y), which should match with the number of equations. So you need 2 equations. For 1) 1 equation, for 2) 1 equation, which is likely to make C the answer. When 1) & 2), 1)=2) -> x=y=0, which is no and sufficient.
Thus, D is the answer.


 For cases where we need 2 more equations, such as original conditions with “2 variables”, or “3 variables and 1 equation”, or “4 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 70% chance that C is the answer, while E has 25% chance. These two are the majority. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer using 1) and 2) separately according to DS definition (It saves us time). Obviously there may be cases where the answer is A, B, D or E.

No, it is equal to 0

Enviado desde mi LG-D855 mediante Tapatalk

But where are the possible answers?

This is a data sufficiency question. Options for DS questions are always the same.

The data sufficiency problem consists of a question and two statements, labeled (1) and (2), in which certain data are given. You have to decide whether the data given in the statements are sufficient for answering the question. Using the data given in the statements, plus your knowledge of mathematics and everyday facts (such as the number of days in July or the meaning of the word counterclockwise), you must indicate whether—

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient to answer the question asked.
C. BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient to answer the question asked.
D. EACH statement ALONE is sufficient to answer the question asked.
E. Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.

I suggest you to go through the following post ALL YOU NEED FOR QUANT.

Hope this helps.

P.S. You can check the OA (Official Answer) under the spoiler in the original post.
_________________

Oh that is why! Thank you so much for your explanation

Enviado desde mi LG-D855 mediante Tapatalk

xy <0

#1
5|x| + |y| = 0
this would be sufficient only when x=y=0 ; sufficient

# 2
|x| + 5|y| = 0

this would be sufficient only when x=y=0 ; sufficient

IMO D

If sum of two +ve terms is zero then both the terms is = 0.

1. 5*0 + 0 =0 xy=0

2. 0 + 5*0 =0 xy=0

D. Either statement independently sufficient.

At first I got confused by looking at option 1.

Both of these options will hold true when x and y are ZERO.

No other value of x and y can make the term ZERO

Is xy < 0?

The statement is asking us whether x and y have opposite signs.

(1) 5|x| + |y| = 0

|x| and |y| are always going to be positive. Pick any number in the universe and you will get a positive quantity.
Given that, for the equation to hold true, x and y MUST be 0.
xy < 0 IS NOT true
Sufficient.

(2) |x| + 5|y| = 0
Same logic as st1.
Sufficient.

D is the answer.
_________________

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________