Suppose you know the area of a circle is approximately
Guidance
Just like in the English language, mathematics uses several words to describe one thing. For example, sum, addition, more than, and plus all mean to add numbers together. The following definition shows an example of this.
Definition: To evaluate means to follow the verbs in the math sentence. Evaluate can also be called simplify or answer.
To begin to evaluate a mathematical expression, you must first substitute a number for the variable.
Definition: To substitute means to replace the variable in the sentence with a value.
Now try out your new vocabulary.
Example A
Evaluate
Solution: Evaluate means to follow the directions, which is to take 7 times
Because algebra uses variables to represent the unknown quantities, the multiplication symbol
Example B
Rewrite
Solution:
It can also be written as
The following is a reallife example that shows the importance of evaluating a mathematical variable.
Example C
To prevent major accidents or injuries, these horses must be fenced in a rectangular pasture. If the dimensions of the pasture are 300 feet by 225 feet, how much fencing should the ranch hand purchase to enclose the pasture?
Solution: Begin by drawing a diagram of the pasture and labeling what you know.
To find the amount of fencing needed, you must add all the sides together:
By substituting the dimensions of the pasture for the variables
Now we must evaluate by adding the values together. The ranch hand must purchase
Guided Practice
1. Write the expression
2. If it costs $9.25 for a movie ticket, how much does it cost for 4 people to see a movie?
Solutions:
1.
2. Since each movie ticket is $9.25, we multiply this price by the 4 people buying tickets to get the total cost:
It costs $37 for 4 people to see a movie.
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: Variable Expressions (12:26)
In 1 – 4, write the expression in a more condensed form by leaving out the multiplication symbol.

2×11x 
1.35⋅y 
3×14 
14⋅z
In 5 – 9, evaluate the expression.

5m+7 whenm=3 
13(c) whenc=63  $8.15(
h ) whenh=40 
(k−11)÷8 whenk=43 
(−2)2+3(j) whenj=−3
In 10 – 17, evaluate the expression. Let

2a+3b 
4c+d 
5ac−2b 
2ac−d 
3bd 
a−4b3c+2d 
1a+b 
abcd
In 18 – 25, evaluate the expression. Let

8x3 
5x26z3 
3z2−5w2 
x2−y2 
z3+w3z3−w3 
2x2−3x2+5x−4 
4w3+3w2−w+2 
3+1z2
In 26 – 30, evaluate the expression in each reallife problem.
 The measurement around the widest part of these holiday bulbs is called their circumference. The formula for circumference is
2(r)π , whereπ≈3.14 andr is the radius of the circle. Suppose the radius is 1.25 inches. Find the circumference.Christmas Baubles by Petr Kratochvil
 The dimensions of a piece of notebook paper are 8.5 inches by 11 inches. Evaluate the writing area of the paper. The formula for area is length
× width.  Sonya purchased 16 cans of soda at $0.99 each. What is the amount Sonya spent on soda?
 Mia works at a job earning $4.75 per hour. How many hours should she work to earn $124.00?
 The area of a square is the side length squared. Evaluate the area of a square with a side length of 10.5 miles.