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Numbers
Before you take the Math IC, you should know the common
types of numbers. Of these types, the most important ones to understand
are probably integers and real numbers. They can be spotted in nearly
every question on the test and will be explicitly mentioned at times.
- Whole Numbers. The set of counting numbers, including zero {0, 1, 2, 3, . . .}.
- Natural Numbers. The set of all whole numbers except zero {1, 2, 3, 4, 5, . . .}.
- Integers. The set of all positive and negative whole numbers, including zero. Fractions and decimals are not included {. . . , –3, –2, –1, 0, 1, 2, 3, . . .}.
- Rational Numbers. The set of all numbers that can be expressed as a quotient of integers. That is, any number that can be expressed in the form m⁄n , where m and n are integers. The set of rational numbers includes all integers and all fractions that can be created using integers in the numerator and denominator.
- Irrational Numbers. The set of all numbers
that cannot be expressed as a quotient of integers. Examples include
π,
, 1.01001000100001000001 . . . . The
sets of irrational numbers and rational numbers are mutually exclusive.
Any given number must be either rational or irrational; no number
can be both. - Real Numbers. Every number on the number line. The set of real numbers includes all rational and irrational numbers.
- Imaginary Numbers. See the “Miscellaneous Math” chapter later in this book.
On the Math IC, integers and real numbers will appear
far more often than any of the other number types.
Even and Odd Numbers
Even numbers are those numbers that are divisible by two
with no remainder.
Only integers can be even or odd, meaning decimals and
fractions are not included. Zero, however, is an integer and thus
a member of the set.
. . . , –6, –4, –2, 0, 2, 4, 6, . . .
Odd numbers are those numbers not evenly divisible by
two.
. . . , –5, –3, –1, 1, 3, 5, . . .
The set of even numbers and the set of odd numbers are
mutually exclusive.
A more rigorous definition of even and odd numbers appears
below:
Even numbers are numbers that can be written
in the form 2n, where n is an integer.
Odd numbers are the numbers that can be written in the form 2n +
1, where n is an integer.
This definition is nothing more than a technical repetition
of the fact that even numbers are divisible by two, and odd numbers
are not. It may come in handy, though, when you need to represent
an even or odd number with a variable.
Operations of Odd and Even Numbers
There are a few basic rules regarding the operations of
odd and even numbers that you should know well. If you grasp the
principles behind the two types of signed numbers, these rules should
all come easily.
Addition:
even + even = even
odd + odd = even
even + odd = odd
Subtraction:
even – even = even
odd – odd = even
even – odd = odd
Multiplication and Division:
even
even = even
even = evenodd
odd = odd
odd = oddeven
odd = even
odd = evenPositive and Negative Numbers
Positive and negative numbers are governed by rules similar
to those that have to do with even and odd numbers. First, for their
quick definitions:
Positive numbers are numbers that are greater
than zero. Negative numbers are numbers that are less than zero.
The number zero is neither positive nor negative.
Operations of Positive and Negative Numbers
The following rules define how positive and negative numbers
operate under various operations.
Addition and Subtraction:
When adding and subtracting negative numbers, it helps
to remember the following:
Adding a negative number is the same as subtracting its
opposite. For example:
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Subtracting a negative number is the same as adding its
opposite. For example:
=.gif)
Multiplication:
positive
positive = positive
positive = positivenegative
negative = positive
negative = positivepositive
negative = negative
negative = negativeDivision:
positive
positive = positive
positive = positivenegative
negative = positive
negative = positivepositive
negative = negative
negative = negativeThe rules for multiplication and division are exactly
the same since any division operation can be written as a form of
multiplication: a
b =
a/b = a 
1/b .
b = Absolute Value
The absolute value of a number is the distance on a number
line between that number and zero. Or, you could think of it as
the positive “version” of every number. The absolute value of a
positive number is that same number, and the absolute value of a
negative number is the opposite of that number.
The absolute value of x is symbolized
by |x|.
Solving an equation with an absolute value in it can be
particularly tricky. As you will see, the answer is often ambiguous.
Take a look at the following equation:
We can simplify the equation in order to isolate |x|:
Knowing that |x| = 2 means
that x = 2 and x = –2 are
both possible solutions to the problem. Keep this in mind; we’ll
deal more with absolute values in equations later on in the Algebra chapter.
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