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No matter how brilliant you are, you need to know the conventions in the field. Math, and particularly GMAT math, has several conventions, definitions, and jargon terms. They are collected in this page.
Top quirks
This is a short list of truisms knowing which can save you from the most common errors:
 0 is not positive, nor negative
 0 is a multiple of every number, and therefore is even
 0 and 1 are neither prime nor composite
 0 is greater than 1
 is undefined

 2 is the only even prime number
Number families
 real
 all numbers on GMAT are real
 integer
 {..., 3, 2, 1, 0, 1, 2, 3, ...}
 fractional
 noninteger reals, such as 3.1417
 whole
 {0, 1, 2, 3, ...}
 even
 {..., 4, 2, 0, 2, 4 ...}
 odd
 {..., 3, 1, 1, 3, ...}
 positive
 any number strictly greater than zero
 negative
 any number strictly less than zero
 perfect squares
 {1, 4, 9, 16, ...}  integer squares of other integers
 prime
 {2, 3, 5, 7, 11, 13, ...}  see below for a definition
 composite
 {4, 6, 8, 9, ..}  nonprime positive integers except 1
Factors and multiples
Suppose (all numbers are whole). Then:
 is a multiple of and of
 and are divisors (factors) of
Prime and composite numbers
The positive integer () is a prime if the only positive divisors of are 1 and itself. The first 10 primes are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29. All other positive integers (except 1) that are not prime are composite numbers.
See also Prime test.