## Year 2 Lesson Plan 6 - Areas of Plane Figures

1. (5 min) Mental Math
1. What is 4 times 6 divided by 2? [12]
2. What is 75% of 200? [150]
3. What is the perimeter of a pentagon whose sides are 3 in? [15 in]
4. What is the perimeter of an equilateral triangle whose sides are 4 in? [12 in.]
5. Take the number of sides in a hexagon, multiply by 10, then divide by 2 [30]

2. (5 min) Review selected problems from lesson 5 (no more than 3 problems)

3. (5 min) Review areas:

Shape
Area Formula
Example
Rectangle
A=b x h
base=13 in
height=3 in
39 sq. in.
Triangle For whole number sides:
A = (b x h)/2

For mixed number or fraction sides:
1/2 x b x h
Ex. 1: base = 24 in and height = 10 in

Ex. 2: base = 1 1/2 in, height = 2 1/2 in
1) 120 sq in.

2) 15/8 = 1 7/8 in.

Trapezoid
B = 6 in.
b = 4 in
h = 2 in.
10 sq. in.
Circle
pi · r · r -or- pi · r2
radius = 4 in 50.24 sq. in.
SPECIAL OBJECTIVE: using different methods to correctly calculate an answer. A trapezoid is a four sided figure that has two sides parallel. There are several ways to figure the area of a trapezoid. One is to make a rectangle and 2 triangles. Another is to make two obtuse triangles. Students may come up with others. It doesn't matter which method you use. It is a good idea to try two different methods to see if you get the same answer both ways.
4. (Remainder of class) In-class exercise

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