Algebraic Expressions

Everyday Math Lesson 10.3

Lesson Objectives• I can identify and use patterns in tables to

solve problems

• I can write algebraic expressions to model rules

• I can use variables to write number models that describe situations

Mental Math

4 + 7 30 + 70 50 + 60

84 + 7 30 + 78 150 + 260

84 + 47 30 + 778 152 + 263

MathMessage( 3 minutes)

Joe and Maria are 5th graders. Joe is 2 inches taller than Maria. Make a

table of 4 possible heights for Joe and Maria.

Math Message Follow-Up(5 minutes)

• How tall is Joe?• What does his height depend

upon?

• How tall is Maria?

Introducing Algebraic Expressions* The table of Maria and Joe’s height is similar to

a “What’s My Rule?” table.– What was the rule for Maria and Joe’s table?

• Let’s represent Joe’s height using an algebraic expression. (“M” represents Maria’s height)M + 2

M M + 2

• Turn to pg. 218 in your SRB.• Study the examples of expressions that algebraic and those

that are not.– What’s the difference????

• Expressions use operation symbols (+, -, *, /) to combine numbers, but algebraic expressions combine variables and numbers.

• KEY POINTS:– A situation can be represented in several ways (words, table, or

symbols)– Algebraic expressions use variables and other symbols to represent

situations– To evaluate an A.E means to substitute values for variables and solve.

Practice!Propose algebraic expressions to fit the situations

• Sue weighs 10 pounds less than Jamal. If J= Jamal’s weight, then J-10 represents Sue’s weight.

• Isaac collected twice as many cans as Alex. If A= the number of cans Alex collected, then 2 * A, (or 2A) represents the number of cans Isaac collected.

• There are half as many problems in today’s assignment as there were in yesterday’s. If Y= the number of problems in yesterday’s assignment, then there are ½ Y, ½ * Y, or Y/2 problems in today’s assignment.

Algebraic Equations

• Expressions can be combined with relation symbols (=, <, >) to make number sentences. – X + 2 = 15– 3y + 7 < 100

* These are called “Algebraic Equations” (number sentences that contain algebraic expressions)

Writing Algebraic Expressions

• Turn to pg. 341 & 342 in your journal.

• Let’s go over problem 1

• Complete the statements on both pages with a partner.• When you are finished, complete the “What’s My

Rule” on pg. 343.

Independent Work• On your own at a level 0, complete Math boxes

on page 344.

• When you are finished, you may work on Study Link 10.3