# 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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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.

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 expression 18n - 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. 0.5 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

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

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

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 month How much will Andy owe if he uses his phone for 90 minutes? \$15 \$18 \$21 \$24

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