Negative numbers are never prime. Neither is zero or one.

The smallest prime number is two, also the only even prime number.

All other prime numbers are odd and all prime numbers greater than 3 are +/- 1 from a multiple of six. Like 11 and 13 on either side of 12 (a multiple of 6) or 29 and 31 on either side of 30 (a multiple of 6) of course not ever number that is +/- 1 from a multiple of 6 is prime (for example 35 is not prime) but these are the only numbers that can be prime.

Tips for strengthen Data Sufficiency:

This is something that all students come to at some point. Data Sufficiency is really about being careful and about not making small mistakes or assumptions.

One thing you can do is to make a list of the five number properties (from the Veritas Data Sufficiency book) and keep this with you until they are second nature.

Five Number Properties:

1) Positive / Negative
2) Odd/ Even
3) Non-integers
4) Prime numbers/ factors
5) O and 1

You should make sure that you at least consider these factors for each question. Some are easier to identify - odd/even is usually very easy to spot since they generally say "odd" or "even" in the question. Positive/ Negative, non-integers, and zero and one you should at least consider each time.


Then there is being careful when you do the problems. I have students write a bit more on data sufficiency. I have them do the same thing on each problem. I call this using the "handrails" and this can help you prevent many of the problems that you mention.

Here is an article that details these handrails: https://www.beatthegmat.com/mba/2012/10/ ... -handrails