Year 2 Lesson Plan 5 - Fraction addition and
perimeter
- (5 min) Mental Math
- What is 25% of 16? [4]
- What is 1/3 of 18? [6]
- What is the decimal equivalent of 1/3? [.333...]
- What is 2/3 + 2/3? Express your answer as a mixed number [1 1/3]
- What is 1/2 of 1/4? [1/8]
- (5 min) Review of selected problems from lesson 4 (no more than 3
problems)
- (5 min) Review of fractions:
- Mixed number conversion to improper fractions: Examples:
1 1/2 = 3/2 2 1/3 = 7/3 3 1/4 = 13/4
Ask: How many halves How many thirds How many fourths
are in 1 1/2? are in 2 1/3? are in 3 1/4?
[3] [7] [13]
- Common denominators: Examples:
- 2/3 + 2/5:
Find a number that both denominators divide into: 3 x 5 = 15
Multiply 2/3 top and bottom by 5 = 10/15
[Reason: to make the new denominator 15]
Multiply 2/5 top and bottom by 3 = 6/15
Add: 10/15 + 6/15 = 16/15 or 1 1/15.
- 1/4 + 5/6
Ask the class: What denominator should we use?
What do we multiply 1/4 by? what do we multiply 5/6 by?
- (10 min) Discuss perimeter [length around the edge of a figure].
- Use this example:
- Discuss perimeter of various shapes:
- Perimeter of a square with sides 5 cm [P=20 cm]
- Perimeter of an equilateral triangle with sides 5 cm [P= 15 cm]
- Perimeter of an isoceles triangle with sides 3,3,4 cm [P= 10 cm]
- Circumference of circle with diameter 5 cm [= pi X diameter = 15.7 cm]
- Perimeter of regular hexagon with sides 5 cm [P= 30 cm]
(hex = six)
- Perimeter of regular octagon with sides 5 cm [P= 40 cm]
(oct = 8 [think: octopus])
- Perimeter of regular pentagon with sides 5 cm [P= 25 cm]
(penta = 5 [think Chrysler symbol])
- (Remainder of class) In-class exercise
- Hand out homework as students successfully complete the in-class exercise.
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