Data Sufficiency

Is rs = rx - 2?
1. r is an odd number
2. x = s + 2

Note: For those of you who have seen this question in the official source, try not to copy the official explanation. Is is not very convincing, hence this query.

(1) r is odd.
Choose r = 1, s = 2, x = 4. Then rs = 2, rx - 2 = 2.
Choose r = 1, s = 2, x = 2. Then rs = 2, rx - 2 = 0.

Insufficient.

(2) x = s + 2. Substitute this into rx - 2 = r (s + 2) - 2 = rs + 2r - 2.

Set this equal to rs and we see this will be valid for rs= rs + 2r - 2 which simplifies to r=1.

Choose r = 1, x = 1, s = -1. Then rs = -1, and rx - 2 = 1 -2 = -1.
Choose r = 3, x = 2, s = 0. Then rs = 0, and rx - 2 = 6 - 2 = 4.

Insufficient.

(1)+(2)
Notice that in (2) we chose r to be odd in both cases. So the argument for (2) applies to this case.

Insufficient.

The answer is E.

raleigh,
I came up with the same answer, but the official answer is B, even though is is true only when r=2.

Came an expert shed some light on this?

My counter example for (2) is correct so it cannot be B.

The OA is incorrect unless you mistyped the problem. Which problem is this in the OG?

I think you misunderstood my point, I did imply that I too think the answer should be E for the very obvious reason that statement 2 is true only for r=2 and not always. Also, there is nothing wrong with the problem as stated.

I understand your point. I'd like to see the actual OA; what book is this from and what is the number for this problem? It has to be wrong.

McGraw Hills GMAT 2009 Practice Test 3: Q27

yes E.
B would have been the answer if it also tells us that r =1; which is is not so.

Answer E

In statement (2), we get r = 1. In the part underlined, you chose r = 3

Is this right? Please clarify.

IMO, you can as well use the same values what you used in Statement (1)

raleigh wrote:(1) r is odd.
Choose r = 1, s = 2, x = 4. Then rs = 2, rx - 2 = 2.
Choose r = 1, s = 2, x = 2. Then rs = 2, rx - 2 = 0.

Insufficient.

(2) x = s + 2. Substitute this into rx - 2 = r (s + 2) - 2 = rs + 2r - 2.

Set this equal to rs and we see this will be valid for rs= rs + 2r - 2 which simplifies to r=1.

Choose r = 1, x = 1, s = -1. Then rs = -1, and rx - 2 = 1 -2 = -1.
Choose r = 3, x = 2, s = 0. Then rs = 0, and rx - 2 = 6 - 2 = 4.

Insufficient.

(1)+(2)
Notice that in (2) we chose r to be odd in both cases. So the argument for (2) applies to this case.

Insufficient.

The answer is E.

r0 + s = r0 + x - 2
s = x -2
x = s +2

STMT I

Does not tell anything about s or x

Insuff

STMT II

this is what the question is asking

Insuff

STMT I & II

Insuff, as we do not know anything about s or x

E