1. Lesson Topic: Replacing Letters with Numbers (Day 1)
Lesson Objective: I can…
Understand that a letter represents one number in an expression.

2. Example 1: Guided Practice

3. * We can count the units in this example.
Example 1 Continued:
What is the length of one side of the square?
What is the formula for the area of the square?
What is the square’s area as a multiplication expression?
What is the square’s area?
* We can count the units in this example.

4. What if the number is too large to count the squares? Then what?
What if the side length of this square is 23 cm?
What expression can we build to find this square’s area?
What is the area of the square?

5. Exercise 1: Independent Practice
S = 25 in.
S = 4
Length of One Side of the Square
Square’s Area Written as an Expression
Square’s Area Written as a Number

6. Example 2: X cm What does the letter b represent in the 1st rectangle?
B cm
8 cm
4cm
What does the letter b represent in the 1st rectangle?
With a partner, answer the following question: Given that the second rectangle is divided into four equal parts, what number does the x represent?
How did you arrive at this answer?
What is the total length of the second rectangle?
If the two large rectangles have equal lengths and widths, find the area of each rectangle.
Discuss with your partner how the formulas for the area of squares and rectangles can be used to evaluate area for the particular figure.

7. Exercise 2:
1st Rectangle: W = 4 L = 7 2nd Rectangle: W = 32cm L = 46cm Complete the table.
Length of Rectangle
Width of Rectangle
Rectangle’s Area Written as an Expression
Rectangle’s Area Written as a Number

8. Example 3:
Look at Example 3 that has been handed out to you. Answer the questions that follow in the handout in your notebook or on your PowerPoint.

9. Exercise 3:
Complete Exercise 3 from your handout in your notebook or on your PowerPoint.

10. Understand that a letter represents one number in an expression.
Let’s Review (Day 2)
Lesson Topic: Replacing Letters with Numbers
Lesson Objective: I can…
Understand that a letter represents one number in an expression.

11. Exercises 1 - 4:
In the drawing below, what do the letters l and w represent? l W

12. Exercises continued: What does the expression l + w + l + w represent?
What does the expression l x w represent?
The rectangle has a length of 5 and a width of 2. Evaluate the expression for questions 2 and 3.

13. Lesson Summary:
EXPRESSION: An expression is a numerical expression, or it is the result of replacing some (or all) of the numbers in a numerical expression with variables. There are two ways to build expressions: 1. We can start out with a numerical expression, like 13∙(2+4)+7, and replace some of the numbers with letters to get 13∙(𝑥𝑥+𝑦𝑦)+𝑧𝑧. 2. We can build such expressions from scratch, as in 𝑥𝑥+𝑥𝑥(𝑦𝑦−𝑧𝑧), and note that if numbers were placed in the expression for the variables 𝑥𝑥, 𝑦𝑦, and 𝑧𝑧, the result would be a numerical expression.

14. Evaluate your learning…
How will you “Sharpen your saw?”