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Is Y odd?

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Is Y odd?

by strain15 » Mon Jun 20, 2011 8:05 pm
Hello, can anyone please help me on this? Thanks a lot. I really appreciate it.

a) If X is divisible by 4, is Y odd?

1) y = x + 3
2) x = 4

[spoiler]Ans: A[/spoiler]

b) If W is divisible by 7, is Z even or odd?

1) Z = W+1
2) W = 7

[spoiler]Ans: E[/spoiler]
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by Ashley@VeritasPrep » Mon Jun 20, 2011 8:19 pm
Hi there,

First question first:
a) If X is divisible by 4, is Y odd?

1) y = x + 3
2) x = 4
This is a good example of a DS question in which much of the thinking work can be done upfront, before even reading the statements. We are told here that X is divisible by 4, so that guarantees that X is even. That's the knowledge we need to be equipped with before we go into the statements.

Now, Statement (1) tells us that y = x + 3, so in other words, y = some even number plus 3. An even plus an odd will ALWAYS give you what? -- an odd. So we're all set with Statement (1).

Statement (2) just tells us x = 4, but it tells us NOTHING about y. So there's no way it will let us answer the question about y.
Last edited by Ashley@VeritasPrep on Tue Jun 21, 2011 4:02 am, edited 2 times in total.
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by Ashley@VeritasPrep » Mon Jun 20, 2011 8:24 pm
Second question: There's a typo somewhere, either in the answer or in the writing of the problem (though the typo may exist in the original material). But the problem as written should not have the answer given. Can you check?
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by Ashley@VeritasPrep » Mon Jun 20, 2011 8:33 pm
Meanwhile, I will assume the problem is indeed
b) If W is divisible by 7, is Z even? (I have taken off the wording "or odd," because the GMAT would write this simply as a yes/no question (i.e. it would either ask "is Z even?" or "is Z odd?").)

1) Z = W+1
2) W = 7
This one is quite similar to the last one, with one key difference: here, we go to the statements not knowing nearly as much. The fact that W is divisible by 7 doesn't guarantee anything one way or the other as to W's oddness or evenness -- or, more generally, being a multiple of an odd number gives no guarantee as to what kind of number you are -- in contrast to being a multiple of an even number, an attribute that guarantees that you yourself are even.

So, when we come to Statement (1) this time, we just know that Z is one more than either an odd or an even number, so it itself could likewise go either way (it will be whatever W is not, in terms of odd or even).

As in the similar problem, Statement (2) here tells us literally nothing about Z, so it's certainly not sufficient alone.

Then, though, when we combine the statements, we literally ascertain a value for Z -- Z = 1 + W and W = 7, so Z = 8. Knowing exactly what Z is clearly enables us to answer the question about whether it is even at this point.
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by strain15 » Mon Jun 20, 2011 8:47 pm
Ashley@VeritasPrep wrote:Hi there,

First question first:
a) If X is divisible by 4, is Y odd?

1) y = x + 3
2) x = 4
This is a good example of a DS question in which much of the thinking work can be done upfront, before even reading the statements. We are told here that X is divisible by 4, so that guarantees that X is even. That' the knowledge we need to be equipped with before we go into the statements.

Now, Statement (1) tells us that y = x + 3, so in other words, y = some even number plus 3. An even plus an odd will ALWAYS give you what? -- an odd. So we're all set with Statement (1).

Statement (2) just tells us x = 4, but it tells us NOTHING about y. So there's no way it will let us answer the question about y.
[/quote]

What if we combine statement 1 and 2 on this question? Wouldn't that work too?
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by strain15 » Mon Jun 20, 2011 8:48 pm
Ashley@VeritasPrep wrote:Second question: There's a typo somewhere, either in the answer or in the writing of the problem (though the typo may exist in the original material). But the problem as written should not have the answer given. Can you check?
Sorry about that, the question actually was asking for odd only. Thanks for the correction.
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by casperkamal » Tue Jun 21, 2011 8:37 am
But for the second question i guess the answer is D. Both statement combined should give the answer
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by Ian Stewart » Tue Jun 21, 2011 1:10 pm
strain15 wrote: What if we combine statement 1 and 2 on this question? Wouldn't that work too?
Whenever one statement is sufficient alone, it will, of course, *always* be possible to answer the question using both statements; after all, you're then using the statement that was sufficient on its own in addition to the information in the other statement. It is crucially important to understand the exact wording of the answer choices in GMAT DS questions. The third answer choice reads:

* BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

So you *only* ever combine the two statements when NEITHER statement is sufficient alone. In the above question, since Statement 1 is sufficient alone, the answer has to be A, and you should never even consider the two statements together.
casperkamal wrote:But for the second question i guess the answer is D. Both statement combined should give the answer
When both statements combined give you the answer, but neither statement alone does, the correct answer is the third answer choice, not the fourth. The answer choices aren't labelled with letters on the actual GMAT, but normally on forums we call the third answer choice 'C'.
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by casperkamal » Tue Jun 21, 2011 7:15 pm
Yeah right. I intended to write "C" as answer but wrote "D" by mistake..
Thanks Ian
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by yjeezle » Tue Jun 21, 2011 7:55 pm
strain15 wrote:Hello, can anyone please help me on this? Thanks a lot. I really appreciate it.

a) If X is divisible by 4, is Y odd?

1) y = x + 3
2) x = 4

[spoiler]Ans: A[/spoiler]

b) If W is divisible by 7, is Z even or odd?

1) Z = W+1
2) W = 7

[spoiler]Ans: E[/spoiler]
the answer for #2 is confirmed to be C correct?
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by strain15 » Tue Jun 21, 2011 8:27 pm
Yes, I believe it was an error on the book. That is why I wanted to double check here. The correct answer should be C. Thanks.
yjeezle wrote:
strain15 wrote:Hello, can anyone please help me on this? Thanks a lot. I really appreciate it.

a) If X is divisible by 4, is Y odd?

1) y = x + 3
2) x = 4

[spoiler]Ans: A[/spoiler]

b) If W is divisible by 7, is Z even or odd?

1) Z = W+1
2) W = 7

[spoiler]Ans: E[/spoiler]
the answer for #2 is confirmed to be C correct?
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