Data Sufficiency

if X>1, what is the value of the integer X?

1. there are X unique factors of X.
2.The sum of X and any prime number larger than X is odd.

The answer is A but i think it should be D

looks like A
(1) here only x=2 looks good. all other integers considering that x>1 failed with this restriction
(2) simply says that x is even
next primes after x are all odd, even +odd=odd, valid for many values of x
say x=2 2+3=5-odd, 2+11=13-odd
x=4, 4+5=9-odd, and so on

Hey Sandeep,

My guess is that you're looking at statement 2 and already embedding what you know about statement 1 somehow.

If you look at statement 2 alone, the only thing that it tells you is that X is even. From the given information, we know that:

X is an integer greater than 1, so x is 2 or above.

From statement 2 we know that:

X + a prime number greater than X (so minimum value 3, since X has a minimum value of 2) is Odd. And we know that Odd + Odd is even, so we need X to be even.

But 4 (an even number greater than 1) plus 7 (a prime number greater than 4) is 11, and odd. So X doesn't HAVE to be 2, although it could be.


My guess is that you're already thinking in terms of prime numbers and therefore looking for an even prime, so you're thinking of 2. But look closely at statement 2 - it only says that X + any PRIME number greater than X is odd. It doesn't say that X itself is prime, even though you're probably already thinking that way. That's where they get you - be extremely careful of assuming or inferring any information that isn't already there.

Brian@VeritasPrep wrote: My guess is that you're already thinking in terms of prime numbers and therefore looking for an even prime, so you're thinking of 2. But look closely at statement 2 - it only says that X + any PRIME number greater than X is odd. It doesn't say that X itself is prime, even though you're probably already thinking that way. That's where they get you - be extremely careful of assuming or inferring any information that isn't already there.

Hey Brian,

Spot on Mate!! i was exactly thinking on the same lines as you described.I thought the only prime even is 2 and that should only give us an ODD number if added with another prime.

Thanks a ton for the explanation

Sandy

Glad that helped, Sandy! And I'm not surprised that that was the mistake you made - what's neat about the GMAT is that you can start to learn how they toy with your mind to get you to make those assumptions. Particularly on Data Sufficiency be really careful with those assumptions and always be skeptical about which knowledge you truly do have. I've always seen it this way - there are really only two ways that they can elicit a wrong answer from you on DS:

1) You think you have enough information, but you actually don't

-this usually comes in the form of an assumption you make (that x is an integer, or positive, or you forget to consider 0)
-it also comes when you prematurely archive the information in statement 1 and use it on statement 2. But you don't know the information from statement 1 when you're looking at "Statement 2 ALONE" so be careful.
-like you saw here, they can also mention a word elsewhere in the question (prime, even, etc.) and get you to start thinking only about that type of number. So be careful with that - if the statement deals with x and y and says that "y is even", make sure that you note "y = even; x = unknown" or something to keep each variable (and what you know about each) straight.

2) You think you don't have enough information, but you actually do

-this can happen when the situation calls for an integer or a positive number (a number of children is always an integer, as you can't have a fractional child; the length of a side of a triangle has to be positive because it can't be negative or 0))
-you should also check for this any time that the answer C seems obvious. Is there a way to derive the information from statement 1 while only using statement 2? They won't too frequently hand you C on a silver platter, so if it looks like they're doing that be careful. This article should give some more information on that: https://www.beatthegmat.com/mba/2010/12/ ... knight-way


As you study, pay attention to the ways they trap you like this and you'll start to look out for them proactively. It's subtle but pretty powerful the way they bait your mind toward thinking only in one direction...