PSSA Math Lesson 22

Evaluating Expressions

D.2.1.3 Determine the value of an D.2.1.3 Determine the value of an algebraic expression by simplifying algebraic expression by simplifying and/or substituting a number for the and/or substituting a number for the variable.variable.

ª An algebraic expression uses numbers and letters to represent a quantity.

ª The letters, called variables, stand for unknown amounts.

ª Youcan find the value of an algebraic expression by determining a value for the variable.

NOTES

Example:

Evaluate 12a - 2 when a = ¾

Substitute and compute:

Example:

A phone company uses this expression to calculate the cost of a phone call: 1.25 + 0.10m. There is a fixed cost of $1.25 and m is the number of minutes of the call. What is the cost of a call that lasts 20 minutes?

Sample Test Questions

What is the value of the expression 3x - 5 when x = 3?

4

5

11

14

What is the value of the expression 2b + 4 when b = ½ ?

0

5

8

10

What is the value of the expression 6.5 - 3z when z = 0.5 ?

1.75

3

5

9

What is the value of the expression ¾ + 2m when m = ¼ ?

1 ¼

2 ½

3

3 ¾

What is the value of the expression18n - 13 when n = 11?

16

42

125

185

What is the value of the expression 1.5t + 1.5 when 1 = 4?

3.5

4.5

5

7.5

A taxi company used this expr3ession to calculate the cost of a ride. 0.5t + 3In this expression, t is the time in minutes and $3 is a fixed charge. What is the cost of a ride that lasts 10 minutes?

$3.50

$6.00

$8.00

$13.50

A computer repair person charges $40 for a house call and $24 per hour. The expression used to find the cost is: 40 + 24tIn this expression, t is the time in hours. What is the cost of a repair if the house call lasts 3 hours?

$64

$88

$112

$144

The cost of a meal at Morales' Deli depends on the weight of the main course. The expression used to find the cost is:5 + (½)wThere is a $5 fixed charge and w is the weight of the main course in ounces. What is the cost of a meal if the main course weighs 18 ounces?

$7.00

$9.00

$11.50

$14.00

Andy's cellular phone company charges a $15 fixed monthly fee. they give 60 free minutes and then charge $0.10 per minute for each additional minute. This expression shows how they find the total monthly cost if there are more than 60 minutes of calls.

15 + 0.10(m - 60), where m is the total minutes each month

How much will Andy owe if he uses his phone for 90 minutes?

15 + 0.10(m - 60), where m is the total minutes each monthHow much will Andy owe if he uses his phone for 90 minutes?

$15

$18

$21

$24