# Foundations

## Fractions


### Simplify Fractions

A fraction is a way to represent parts of a whole. The fraction  represents two of three equal parts. See . In the fraction  the 2 is called the numerator and the 3 is called the denominator. The line is called the fraction bar.
Fractions that have the same value are equivalent fractions. The Equivalent Fractions
Property allows us to find equivalent fractions and also simplify fractions.
A fraction is considered simplified if there are no common factors, other than 1, in its numerator and denominator.
For example,
   is simplified because there are no common factors of 2 and 
   is not simplified because 5 is a common factor of 10 and 
We simplify, or reduce, a fraction by removing the common factors of the numerator and denominator. A fraction is not simplified until all common factors have been removed. If an expression has fractions, it is not completely simplified until the fractions are simplified.
Sometimes it may not be easy to find common factors of the numerator and denominator. When this happens, a good idea is to factor the numerator and the denominator into prime numbers. Then divide out the common factors using the Equivalent Fractions Property.
We now summarize the steps you should follow to simplify fractions.

### Multiply and Divide Fractions

Many people find multiplying and dividing fractions easier than adding and subtracting fractions.
To multiply fractions, we multiply the numerators and multiply the denominators.
When multiplying fractions, the properties of positive and negative numbers still apply, of course. It is a good idea to determine the sign of the product as the first step. In , we will multiply a negative by a negative, so the product will be positive.
When multiplying a fraction by an integer, it may be helpful to write the integer as a fraction. Any integer, a, can be written as  So, for example, 
Now that we know how to multiply fractions, we are almost ready to divide. Before we can do that, we need some vocabulary. The reciprocal of a fraction is found by inverting the fraction, placing the numerator in the denominator and the denominator in the numerator. The reciprocal of  is  Since 4 is written in fraction form as  the reciprocal of 4 is 
To divide fractions, we multiply the first fraction by the reciprocal of the second.
We need to say   and  to be sure we don’t divide by zero!
The numerators or denominators of some fractions contain fractions themselves. A fraction in which the numerator or the denominator is a fraction is called a complex fraction.
Some examples of complex fractions are:
To simplify a complex fraction, remember that the fraction bar means division. For example, the complex fraction  means 

### Add and Subtract Fractions

When we multiplied fractions, we just multiplied the numerators and multiplied the denominators right straight across. To add or subtract fractions, they must have a common denominator.
The least common denominator (LCD) of two fractions is the smallest number that can be used as a common denominator of the fractions. The LCD of the two fractions is the least common multiple (LCM) of their denominators.
After we find the least common denominator of two fractions, we convert the fractions to equivalent fractions with the LCD. Putting these steps together allows us to add and subtract fractions because their denominators will be the same!
We now have all four operations for fractions.  summarizes fraction operations.
When starting an exercise, always identify the operation and then recall the methods needed for that operation.

### Use the Order of Operations to Simplify Fractions

The fraction bar in a fraction acts as grouping symbol. The order of operations then tells us to simplify the numerator and then the denominator. Then we divide.
Where does the negative sign go in a fraction? Usually the negative sign is in front of the fraction, but you will sometimes see a fraction with a negative numerator, or sometimes with a negative denominator. Remember that fractions represent division. When the numerator and denominator have different signs, the quotient is negative.
Now we’ll look at complex fractions where the numerator or denominator contains an expression that can be simplified. So we first must completely simplify the numerator and denominator separately using the order of operations. Then we divide the numerator by the denominator as the fraction bar means division.

### Evaluate Variable Expressions with Fractions

We have evaluated expressions before, but now we can evaluate expressions with fractions. Remember, to evaluate an expression, we substitute the value of the variable into the expression and then simplify.

### Key Concepts

1. Equivalent Fractions Property
If a, b, and c are numbers where  then

2. How to simplify a fraction.


3. Fraction Multiplication
If a, b, c, and d are numbers where  and  then

To multiply fractions, multiply the numerators and multiply the denominators.
4. Fraction Division
If a, b, c, and d are numbers where  and  then

To divide fractions, we multiply the first fraction by the reciprocal of the second.
5. Fraction Addition and Subtraction
If a, b, and c are numbers where  then

To add or subtract fractions, add or subtract the numerators and place the result over the common denominator.
6. How to add or subtract fractions.


7. How to simplify an expression with a fraction bar.


8. Placement of Negative Sign in a Fraction
For any positive numbers a and b,

9. How to simplify complex fractions.



### Practice Makes Perfect

Simplify Fractions
In the following exercises, simplify.
Multiply and Divide Fractions
In the following exercises, perform the indicated operation.
In the following exercises, simplify.
Add and Subtract Fractions
In the following exercises, add or subtract.
Use the Order of Operations to Simplify Fractions
In the following exercises, simplify.
Mixed Practice
In the following exercises, simplify.
Evaluate Variable Expressions with Fractions
In the following exercises, evaluate.

### Writing Exercises


### Self Check

ⓐ After completing the exercises, use this checklist to evaluate your mastery of the objectives of this section.
ⓑ What does this checklist tell you about your mastery of this section? What steps will you take to improve?