Lesson Plan # 18 - Percents, Multiple
Probabilities
- (5 min) Mental Math
- What is one third of one fourth? [1/12]
- What is the perimeter of a square whose side is 4 1/2 inches? [18 in]
- What is 600 times 800? [480000]
- What is 200 times 80 [16000]
- What is the area of a triangle whose base is 7 inches and whose
height is 6 inches? [21 sq. in.]
- (5 min) Review of homework #16 (<= 3 problems)
- (5 min) Introduce percents:
- The general idea:
- All = 100% = 1/1
- Empty/none = 0% = 0
- Half = 50% = 1/2
- Draw this scale on the board:
100% - +---+ -> 1 = full
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75% - | | -> 3/4
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50% - | | -> 1/2 = half
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25% - | | -> 1/4
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0% +---+ -> 0 = empty
- Use the above scale to contrast percents to fractions:
- 25% = 25/100 = 1/4 = .25
- 75% = 75/100 = 3/4 = .75
- Show that dividing the numerator by the denominator of a fraction
produces a decimal, using 1/4 as an example
Show that percent = decimal * 100 using this same example
Have students convert 3/4 to a decimal, then to a percent by multiplying
by 100.
If time permits, have students convert the following fractions to
percents:
- (15 min) In-class exercise, page 1 only
- (10 min) Explain multiple probabilities:
- Handout "Multiple Probabilities" handout. Follow the discussion in the
handout. Students usually readily see the multiple coin flip example but
have problems with the card examples, especially constructing the
second card probability when the first card is not replaced. Go over that
example CAREFULLY!
- Emphasize again that they
are to multiply (not add) probabilities of independent things together.
- (Remainder of class) In-class Exercise, page 2
- Hand out homework as students successfully complete the in-class
exercise.
Note: This lesson does not explore the meaning of independence. It is
assumed in all problems presented. The second year course will explore
independence more fully.
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