Does set S contain any even numbers? Does the integer k have

[dheeraj787]

Hi Ron,

When practicing GMAT PREP questions, I have identified a pattern that there is a certain type of DS questions which i always do wrong. When i reviewed, I found that everytime I made a mistake because i could not actually understand the question. Below I will write 2 different questions (Which i faced one after another) and after each questions I will write what i understood,is being asked, and will also write what was actually asked, which i realised when I saw the solution over internet.

I need your help on what should I do to overcome this weakness of not understanding these type of DS question stem;

Q1. Does set S contain any even numbers?
(1) There are no prime numbers in S.
(2) There are no multiples of 4 is S.

What I understood: Does "at least one" set S contain any even number ? So i took a sufficient case as: if I am able to find at least one set which contain any even numbers using the statements then I am done. and therefore I ended up marking the answer of this question "D" which became wrong.

What did the question actually mean: and when i saw the solution, I understood that the question was actually asking that "Will set S always contain any even number" provided the statements given. and then i realised that i understood the question wrong way.


Q2. Does the integer K have a factor p such that 1<p<k ?
(1) K>4!
(2) 13!+2<=k<=13!+13

What I understood: i understood that even if i find at least one k which has factor p such that 1 < p < k then that is sufficient. so I said ok then from Statement 1 there is 25 which has 1,5,25 as factors so K=25 so i am done. statement 1 s sufficient. similarly i thought about statement 2.

What did the question actually mean: and when i saw the solution i found that they were actually asking will it hold true in all the possible K's provided given statements.


So this is becoming my weakness now and I am doing all these types of DS questions wrong just because everytime I grasp wrong meaning of the question stem. even after realising and noting down my mistake in first question, I did the same type of mistake in Question 2.

Please suggest how can I overcome this and enhance my understanding of this type of DS questions.

Thanks in advance.
Dheeraj

[RonPurewal]

Hi,
This thread doesn't follow the forum rules; there are two questions in one thread.

The problem here has nothing to do with misreading the statements. The problem is that you haven't yet learned what "not sufficient" and "sufficient" mean.
In other words, you've skipped over understanding the basic fundamentals of DS, probably out of some misguided desire to start solving "hard" problems.

"Not sufficient" means that there are two or more different answers to a question.
"Sufficient" means that there is only one answer, and that it's impossible to find a second answer.

In yes/no questions:

* "Not sufficient" means that you can get "yes" AND you can get "no".

* "Sufficient" means you CAN'T get both of these. You're stuck with just one of them.

Your goal, in these situations, is to see whether you can get "not sufficient" -- i.e., whether you can get BOTH "yes" AND "no".

In the first question, the first statement is not sufficient, because you can get "yes" (e.g., 4, 6, 8) and you can also get "no" (e.g., 9, 15, 21).
The second statement is also not sufficient, since you can get "yes" (if your list contains, say, 6) and you can also get "no" (e.g., 9, 15, 21) again.

Together, still not sufficient, since, with both requirements, you can still get "yes" (e.g., 6, 9, 10) and also "no" (e.g., 9, 15, 21).

[RonPurewal]

The second question I'll leave alone, since the forum rules state that you should post one question per thread. If you have questions about that one, please re-post it as a separate thread.
Thanks.