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PSSA Math Lesson 22 Evaluating Expressions D.2.1.3 Determine the value of an algebraic expression by simplifying and/or substituting a number for the 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 expression 18n - 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. 0.5 t + 3 In 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 + 24 t In 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)w There 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 month How much will Andy owe if he uses his phone for 90 minutes? $15 $18 $21 $24

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