## Year 2 Lesson Plan 12 - Order of Operations

1. (5 min) Mental Math
1. What is 5 squared minus 4 squared?[9]
2. What is the perimeter of a regular hexagon with sides 9 ft long?[54 ft]
3. What is the area of a triangle whose base is 9 inches and whose height is 3 in? [13 1/2 sq. in.]
4. What is 3 cubed minus 3 squared [18]
5. Express 6 feet minus 3 inches in inches [69 in]
2. (5 min) Review multiplication of positive and negative numbers: First do the multiplication, then figure out the sign. If there are an even number of negative signs, then the answer is positive
If there are an odd number of negative signs, then the answer is negative.
Examples:
1. (+3) x (+4) = +12
2. (+3) x (-4) = -12
3. (-3) x (-4) x (-3) = -36 (odd number of - signs)
4. (-3) x (-4) = +12
5. (-3) x (+4) = -12
Note: you may want to ask students to solve the above problems.
3. (10 min) Order of operations for evaluations.
Rules:
• Perform operations from left to right for equivalent operations
• If you have parentheses, do the computations within the parentheses first (just like square root).
• Do exponents and square roots next. Point out that the square root sign extends over everything inside it.
• Next do multiplies and divides.
• Next (and finally) do adds and subtracts.

Use these examples:
1. 32 x 23 = 9 x 8 = 72
2. 2 x 3 + 4 x 5 = 6 + 20 = 26
3. 2 x (3 + 4 x 5) = 2 x (3 + 20) = 2 x 23 = 46
4. 22 x 32 x 42 + 52 = 576 + 25 = 601
5. 10 + 3 x 42 = 10 + 3 x 16 = 10 + 48 = 58

4. (Remainder of class) In-class exercise

5. Hand out homework as students successfully complete the in-class exercise.