## Year 2 Lesson Plan 12 - Order of
Operations

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- (5 min) Mental Math
- What is 5 squared minus 4 squared?[9]
- What is the perimeter of a regular hexagon with sides 9 ft long?[54
ft]
- What is the area of a triangle whose base is 9 inches and whose
height is 3 in? [13 1/2 sq. in.]
- What is 3 cubed minus 3 squared [18]
- Express 6 feet minus 3 inches in inches [69 in]

- (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:

- (+3) x (+4) = +12
- (+3) x (-4) = -12
- (-3) x (-4) x (-3) = -36 (odd number of - signs)
- (-3) x (-4) = +12
- (-3) x (+4) = -12

Note: you may want to ask students to solve the above problems.
- (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:
- 3
^{2} x 2^{3} = 9 x 8 = 72
- 2 x 3 + 4 x 5 = 6 + 20 = 26
- 2 x (3 + 4 x 5) = 2 x (3 + 20) = 2 x 23 = 46
- 2
^{2} x 3^{2} x 4^{2} + 5^{2} = 576 +
25 = 601
- 10 + 3 x 4
^{2} = 10 + 3 x 16 = 10 + 48 = 58

- (Remainder of class) In-class exercise

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