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PRE-ALGEBRA
Lesson 1-3 Warm-Up
PRE-ALGEBRA
Writing and Evaluating
Expressions (1-3)
How do you evaluate an
algebraic expression?
To evaluate an algebraic expression, replace the varaibles (letters) with the numbers
they equal and solve using PEMDAS.
Example: Evaluate 4y - 15 for y = 9
4 (9) - 15
36 - 15
Step 1: Replace the variable with the number
equals.
Step 2: Solve using order of operations [PEMDAS]
21
Example: Evaluate 3ab + c /2 for a =2, b = 5, and c = 10
3(2)(5) + 10 / 2
Step 1: Replace the variable with the number it
equals.
30 + 5
Step 2: Solve using order of operations [PEMDAS]
35
PRE-ALGEBRA
Writing and Evaluating Expressions
LESSON 1-3
Additional Example
Evaluate 18 + 2g for g = 3.
18 + 2g = 18 + 2(3)
Replace g with 3.
= 18 + 6
Multiply.
= 24
Add.
PRE-ALGEBRA
Writing and Evaluating Expressions
LESSON 1-3
Additional Example
Evaluate 2ab – c for a = 3, b = 4, and c = 9.
3
2ab – c = 2(3)(4) – (9) Replace the variables.
3
3
=
=
24
– 3
21
Multiply and divide from left to right.
Subtract
PRE-ALGEBRA
Writing and Evaluating
Expressions (1-3)
Example: An online store charges $14 for each CD and $6 per order. How much
would it cost to order 8 CDs?
Number of CD s
1
2
4
8
Cost of CD s
1 x 14
2 x 14
4 x 14
8 x 14
Shipping
6
6
6
6
Total Cost
1 x 14 + 6 = 14 + 6 = 20
2 x 14 + 6 = 28 + 6 = 34
4 x 14 + 6 = 56 + 6 = 62
8 x 14 + 6 = 112 + 6 = 118
Step 1: Create a table to find the pattern (see above).
n x 14 + 6
Step 2: Write an expression using the pattern
(8) x 14 + 6
Step 3: Replace the variable with the number it equals
112 + 6
Step 4: Solve using order of operations [PEMDAS]
118
PRE-ALGEBRA
Writing and Evaluating Expressions
LESSON 1-3
Additional Example
The Omelet Café buys cases of 36 oranges.
a.
b.
a. x oranges
Write an algebraic expression for the number of
cases the Café should buy for x oranges.
Evaluate the expression for 180 oranges.
x
36
b. 180 oranges
x
(180)
=
36
36
= 5
Evaluate for x = 180.
Divide.
The Omelet Café should buy 5 cases to get 180 oranges.
PRE-ALGEBRA
Writing and Evaluating Expressions
LESSON 1-3
Additional Example
The One Pizza restaurant makes only one kind of
pizza, which costs $16. The delivery charge is $2 per delivery.
Write an algebraic expression for the cost of having pizzas
delivered. Evaluate the expression to find the cost of having
two pizzas delivered.
Words
$16
for each
Let p
Expression
16
pizza
plus
$2 delivery charge
+
2
= number of pizzas.
•
p
Evaluate the expression for p = 2.
16 • p + 2 = 16 • (2) + 2
= 32 + 2
= 34
It costs $34 to have two pizzas delivered.
PRE-ALGEBRA
Writing and Evaluating Expressions
LESSON 1-3
Lesson Quiz
Evaluate.
1. 7(b) – 4 for b = 3
17
3. 3c + 4 ÷ d for c = 8, d = 2
26
2. h ÷ 2 + 1 for h = 12
7
4. fg – g for f = 5, g = 7
28
5. Pens are sold at the school store in packages of 4. Write an
algebraic expression for the number of packages a student
should buy to get p pens. Evaluate this expression for 12 pens.
p 12
;
= 3 packages
4
4
PRE-ALGEBRA