pssa math lesson 22 evaluating expressions d.2.1.3 determine the value of an algebraic expression by...

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