2.9: When to Use the Distributive Property
David and Denise are having an argument. David says that you can't use the Distributive Property to simplify the expression
Guidance
Identifying Expressions Involving the Distributive Property
The Distributive Property often appears in expressions, and many times it does not involve parentheses as grouping symbols. In a previous Concept, we saw how the fraction bar acts as a grouping symbol. The following example involves using the Distributive Property with fractions.
Example A
Simplify
Solution:
The denominator needs to be distributed to each part of the expression in the numerator.
We can rewrite the expression so that we can see how the Distributive Property should be used:
Example B
Simplify
Solution:
Think of the denominator as
Now apply the Distributive Property:
Simplified:
Solve RealWorld Problems Using the Distributive Property
The Distributive Property is one of the most common mathematical properties seen in everyday life. It crops up in business and in geometry. Anytime we have two or more groups of objects, the Distributive Property can help us solve for an unknown.
Example C
An octagonal gazebo is to be built as shown below. Building code requires fivefootlong steel supports to be added along the base and fourfootlong steel supports to be added to the roofline of the gazebo. What length of steel will be required to complete the project?
Solution: Each side will require two lengths, one of five and one of four feet respectively. There are eight sides, so here is our equation.
Steel required
We can use the Distributive Property to find the total amount of steel.
Steel required
A total of 72 feet of steel is needed for this project.
Guided Practice
Simplify
Solution:
First we rewrite the expression so we can see how to distribute the denominator:
Practice
Sample explanations for some of the practice exercises below are available by viewing the following video. Note that there is not always a match between the number of the practice exercise in the video and the number of the practice exercise listed in the following exercise set. However, the practice exercise is the same in both. CK12 Basic Algebra: Distributive Property (5:39)
Use the Distributive Property to simplify the following expressions.

(2−j)(−6) 
(r+3)(−5) 
6+(x−5)+7
Use the Distributive Property to simplify the following fractions.

8x+124 
9x+123 
11x+122 
3y+26 
−6z−23 
7−6p3
In 10 – 17, write an expression for each phrase.

23 times the quantity ofn plus 16  Twice the quantity of
m minus 3 
−4x times the quantity ofx plus 2  A bookshelf has five shelves, and each shelf contains seven poetry books and eleven novels. How many of each type of book does the bookcase contain?
 Use the Distributive Property to show how to simplify 6(19.99) in your head.
 A student rewrote
4(9x+10) as36x+10 . Explain the student’s error.  Use the Distributive Property to simplify 9(5998) in your head.
 Amar is making giant holiday cookies for his friends at school. He makes each cookie with 6 oz of cookie dough and decorates each one with macadamia nuts. If Amar has 5 lbs of cookie dough
(1 lb=16 oz) and 60 macadamia nuts, calculate the following. How many (full) cookies can he make?
 How many macadamia nuts can he put on each cookie if each is supposed to be identical?
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Here you'll learn when to simplify an expression in the form @$\begin{align*}M(N+K)\end{align*}@$ or @$\begin{align*}M(NK)\end{align*}@$ by using the Distributive Property.