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 and decimal tenths

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 4.5m becomes 4.5(m) and then 4.5(7) when m = 7. The operation between 4.5 and (7) is understood to be multiplication.

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

Bring students to the guided group.

Provide students with the variable equation n X 4 = 12.

Ask students:

• What is n?

• How do you know?

• How did you solve it?

Now provide students with the following equation 7 X n + s = 29.

Ask students to try to solve s. Remind them they already solved n.

Tell students that we use one variable equation to help us solve an equation with two variables. - Ask students to create their own variable problems (like the model) to share with a partner to solve.

Take up the worksheet together as a group.

Ask the group:

• How did you find the missing variables?

• How does one variable equation help you solve the second?

• What operations did you use?

• How did you know which operation to use?

Observe students to assess how well they:

• explain concepts related to variables

• use appropriate strategies to solve algebraic equations

• explain their strategies

• use appropriate estimation strategies.

SEL Self-Assessments (English) and Teacher Rubric