Integers

Digits

Digits are the first concept of integers. There are ten digits namely: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

In our number system, the position of the digits are important. For example, consider the number 3,027. This can be represented in a place value table as follows:

Thousands

Hundreds

Tens

Units/Ones

3

0

2

7

For the SAT, the units digit and the ones digit refer to the same digit in a number.

Integers

Integers are whole numbers, for example, –4, –3, –2, –1, 0, 1, 2, 3, 4, ...

Positive integers are all the whole numbers greater than zero, ie: 1, 2, 3, 4, 5, ... We say that its sign is positive. Negative integers are all the whole numbers less than zero, ie: –1, –2, –3, –4, –5, ... We say that its sign is negative.

Integers extend infinitely in both positive and negative direction. This can be represented on the number line.

Zero is an integer that is neither positive nor negative.

Consecutive Integers

Consecutive integers are integers that follow in sequence, each number being 1 more than the previous number, for example 22, 23, 24, 25, ...

Consecutive integers can be more generally represented by n, n +1, n + 2, n + 3, ..., where n is any integer.

Even and Odd Integers

Even integers are integers that can be divided evenly by 2, for example, –4, –2, 0, 2, 4, ... An even integer always ends in 0, 2, 4, 6, or 8.

Zero is considered an even integer. Odd integers are integers that cannot be divided evenly by 2, for example, –5, –3, –1, 1, 3, 5, ... An odd integer always ends in 1, 3, 5, 7, or 9. To tell whether an integer is even or odd, look at the digit in the ones place. That single digit will tell you whether the entire integer is odd or even, for example the integer 3,255 is an odd integer because it ends in 5, an odd integer. Likewise, 702 is an even integer because it ends in 2.

Operations On Even and Odd Integers

Addition	examples:
even + even = even	2 + 4 = 6
odd + odd = even	1 + 3 = 4
odd + even = odd	1 + 2 = 3

Multiplication	examples:
even × even = even	2 × 4 = 8
odd × odd = odd	1 × 3 = 3
odd × even = even	3 × 2 = 6

Prime Numbers

A prime number is a positive integer that has exactly two factors, 1 and itself, for example 29 has exactly two factors which are 1 and 29. So 29 is a prime number.

On the other hand, 28 has six factors which are 1, 2, 4, 7, 14, and 28. So 28 is not a prime number. It is called a composite number. Some examples of prime numbers are: 2, 3, 5, 7, 11, 13, 17, 19, ... Since the number 1 has only one factor (namely 1 itself), it is not a prime number.

The number 2 is the only prime that is even. Other even numbers will have 2 have as a factor and so will not be a prime.

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