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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.
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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
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Example:
Evaluate 12a - 2 when a = ¾
Substitute and compute:
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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?
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Sample Test Questions
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What is the value of the expression 3x - 5 when x = 3?
4
5
11
14
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What is the value of the expression 2b + 4 when b = ½ ?
0
5
8
10
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What is the value of the expression 6.5 - 3z when z = 0.5 ?
1.75
3
5
9
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What is the value of the expression ¾ + 2m when m = ¼ ?
1 ¼
2 ½
3
3 ¾
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What is the value of the expression18n - 13 when n = 11?
16
42
125
185
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What is the value of the expression 1.5t + 1.5 when 1 = 4?
3.5
4.5
5
7.5
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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
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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
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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
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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?
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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