1. 1.1 What you should learn Why you should learn it Variables in Algebra
GOAL 1
Evaluate a variable expression.
GOAL 2
Write a variable expression that models a real-life situation.
Why you should learn it
To express real-life number relationships.

2. 1.1 Variables in Algebra 1 GOAL EVALUATING VARIABLE EXPRESSIONS
VOCABULARY
variable
values
variable expression
evaluating an expression

3. To evaluate a variable expression, follow these three steps:
Write the variable expression.
Substitute values for variables.
Simplify the numerical expression.
EXAMPLE 1

4. Extra Example 1
Evaluate each expression when y = 3. Click for solutions.
1. 4y y y
EXAMPLE 2

5. Extra Example 2
Find the average speed, of a car that traveled 89 miles in 2 hours.
Solution:
average speed
44.5 mi/h
EXAMPLE 3

6. Extra Example 3
Find the perimeter, a + b + c, of the triangle. The dimensions are in centimeters.
Click to see the solution.
a = 1
b = 1.75
c = 2.25
Perimeter = a + b + c = =
5 cm

7. Checkpoint
1. Find the average speed of a car that travels 225 miles in 4.5 hours.
50 mi/h
Find the perimeter of the triangle. The dimensions are in inches. Click for the answers.
c = 6.7
a = 8
b = 8
EXAMPLE 4
22.7 in

8. convert the interest rate
Extra Example 4
Find the simple interest, Prt, you will earn in two years on a deposit of $870 at a rate of 5% per year.
Click for the solution.
Simple interest = Prt =
Did you remember to
convert the interest rate
to a decimal number?
These units
cancel.
$87

9. 1.1 Variables in Algebra 2 GOAL MODELING A REAL-LIFE SITUATION
VOCABULARY
Unit Analysis
Verbal Model
EXAMPLE 5

10. Extra Example 5
You plan to ride your bicycle to school and back at an average rate of 6 miles per hour for a distance of 10.5 miles. How long will it take you? Click to see the solution.
VERBAL
MODEL
LABELS
ALGEBRAIC MODEL
Time =
Time = t
Distance = 10.5 miles
Rate = 6 mi/h
1.75 hours

11. Checkpoint
1. Find the simple interest you will earn after one half of a year with a deposit of $1250 at a rate of 6% per year.
$37.50
Your parents drive to the grocery store 9 miles away at 12:30 p.m. and return at 2:00 p.m. If the grocery shopping took 45 minutes, what was the average speed of their car?
Click for the answers.
24 mi/h

12. QUESTIONS?