From GMATClub
GMAT Study Guide - a prep wikibook
index - edit - roadmap
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
- non-integer 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, ..} - non-prime 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.
