Big Idea:

Using variables is a way to efficiently and generally describe relationships that can also be described using words.

Expectations:

C2.2 evaluate algebraic expressions that involve whole numbers

teacher background

Key concepts

• To evaluate an algebraic expression, the variables are replaced with numerical values and calculations are performed based on the order of operations.

Note

• When students are working with formulas, they are evaluating expressions.

• Replacing the variables with numerical values often requires the use of brackets. For example, the expression 4s becomes 4(s) and then 4(5) when s = 5. The operation between 4 and (5) is understood to be multiplication.

• Many coding applications involve algebraic expressions being evaluated, and this may be carried out in several steps. For example, the instruction: “input ‘the side of a square’, side A” is instructing the computer to define the variable side A and store whatever the user inputs into the temporary location called side A. The instruction: “calculate 4*sideA, perimeter A” instructs the computer to take the value that is stored in “sideA” and multiply it by 4, and then store that result in the temporary location, which is another variable, called perimeter A.

Bring students to the guided table. Discuss with students the following equation: x + 5 = 9.

Ask students to identify the value of x. "How do you know that is the value of x?"

Show students the cue cards; x+5<9 and x+5>9.

• Does x still equal 4?

• Why or why not?

• What could x be?

• Why isn’t it the same value?

• Why are there a lot of possibilities for x?

Provide students with the other cards. Have them solve for x using the equality and inequality signs.

Students will work on Finding the Missing Variables ; independently.

Do the first one as a group to ensure that students understand how to solve these types of problems.

Provide students about 10 minutes to work on this, while at the guided group. Observe student behaviours, and ask prompting questions to ensure student understanding.

Take up the worksheet together as a group.

Ask the group:

• How did you go about solving these problems?

• How did you ensure that they were worth the same?

• Did you have any challenges when solving these equations?

Observe students to assess how well they:

• Solved the Problems

• Ensured that the values were worth the same

• Explained their strategies

• Understood the problem and formulated an approach to solving it.