Which of these two is the greater, x or y?

[rs2010]

23. Which of these two is the greater, x or y?
x – y less than 0
x + y greater than 0
A. 1 alone, not 2 alone
B. 2 alone, not 1 alone
C. 1 and 2 together (need both) Answer
D. 1 alone or 2 alone
E. 1 and 2 together are not sufficient

I selected A but OA is E.

From "How to pass the GMAT" by Mike Bryon.

he he template was not allowing me to add sings



One more

Which of these two is the greater, x or y?
(1) 1/x > 1/y
(2) Both are negative
A. 1 alone, not 2 alone
B. 2 alone, not 1 alone
C. 1 and 2 together (need both) Answer
D. 1 alone or 2 alone
E. 1 and 2 together are not sufficient

OA is C, I selected A

[target790]

First question has some typo.


2nd question>You considered (a) just thinking of positive values.Consider negative values ,you will come down to C immediately.It's only the combination of both which leads to valid conclusion.


Cheers

[rs2010]

I am deducing 1/x > 1/y to y > x.

What's wrong with that ?

[target790]

nothing wrong if you are considering both the numbers positive or both negative.Only when the signs are different we need to be careful.

say:

1/x>1/y =>y>x (only if signs are identical)
1/x>1/y =>y<x(if signs are different)

Hope I'm clear this time.

[Ian Stewart]

I am deducing 1/x > 1/y to y > x.

What's wrong with that ?

You are multiplying both sides of the inequality by xy. If xy is negative, you would need to reverse the inequality. If xy is positive, then your conclusion is valid.

And for this question:

23. Which of these two is the greater, x or y?
x – y less than 0
x + y greater than 0

if x-y < 0, then certainly x < y (add y to both sides). 1) is certainly sufficient here. 2) is clearly insufficient, so the answer should be A.

I'm not familiar with the source, so cannot comment on whether it's worthwhile to be using it for study, but if it contains a lot of mistaken questions like this one, I'd suggest you look elsewhere. When I say that the question is in error, I'm assuming you've transcribed the question and OA correctly.

[rs2010]

Thanks Target790 believe me I did not want to write this name.

I was not condisering the case with diffrent signs.

Thanks Ian too.
I too realized later after finding so many mistakes in the book.
Initially I thought may be I am wrong so I asked couple of those questions here.

I was not practicing anything for maths so I thought of trying my hand on that book.