Set Notation And Probability Diagrams
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Lesson notes
Two-Way Tables
- A two-way table compares two characteristics (e.g., year group and language choice).
- Add row and column totals, including an overall total in the bottom-right corner.
- Probability from the whole table: denominator is the overall total.
- Probability from a specific category: denominator is that category total.
- Always check that row and column totals sum to the overall total.
Two-way table: language choice by year group
Set Notation
- ℰ (or U, ξ) is the universal set – everything under consideration.
- n(A) is the number of elements in set A.
- A ∩ B is the intersection – elements in both A and B.
- A ∪ B is the union – elements in A or B or both.
- A' is the complement – elements in ℰ not in A.
- Sets can be described using curly brackets: {x : rule}.
Venn Diagrams
- A Venn diagram uses a rectangle (ℰ) and circles for sets.
- Overlapping circles show the intersection of sets.
- Place numbers or elements in each region, starting with the intersection.
- Work outwards from the intersection to fill the rest.
Sets A and B
Probabilities from Venn Diagrams
- Probability = (number of elements in region) / (total number of elements).
- For conditional probability, restrict the denominator to the given set.
- Be careful: some given numbers may need to be split between regions.
Spanish and German study (class of 30)
Probability Tree Diagrams
- Tree diagrams show outcomes of repeated experiments with two outcomes each.
- Probabilities on branches from the same point add to 1.
- Multiply along branches to find the probability of a sequence.
- Add probabilities of different sequences to find the probability of combined events.
- For 'at least one', it is often easier to use 1 − P(none).
Two sets of traffic lights
Combined Probability
- P(A and B) = P(A) × P(B) (the 'and rule') for independent events.
- P(A or B) = P(A) + P(B) (the 'or rule') for mutually exclusive events.
- Events are independent if one does not affect the other.
- For 'without replacement', events are not independent – adjust probabilities accordingly.
Slides
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Practice questions
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1.ℰ = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}. A = {1, 4, 9}. What is n(A)?
Easy- A3
- B4
- C5
- D6
2.Which set notation describes the shaded region in a Venn diagram where only the overlap of A and B is shaded?
Easy- AA ∩ B
- BA ∪ B
- CA'
- DB'
3.In a Venn diagram, the universal set is represented by a:
Easy- Arectangle
- Bcircle
- Ctriangle
- Dsquare
4.If P(rain) = 1/3 and P(go fishing | rain) = 3/5, what is P(rain and go fishing)?
Medium- A1/5
- B3/15
- C2/5
- D1/3
5.In a two-way table, the overall total should be placed in which corner?
Easy- Abottom-right
- Btop-left
- Cbottom-left
- Dtop-right
6.ℰ = {1,2,3,4,5,6,7,8,9,10,11,12,13,14}. F = {x: x is a factor of 14}. P = {x: x is a prime number less than 14}. What is n(F ∩ P)?
Medium- A2
- B3
- C4
- D5
7.In a group of 40 students, 24 like football, 19 like cricket, and 10 like football but not cricket. How many students like both football and cricket?
Medium- A14
- B5
- C10
- D9
8.The probability that Arun plays football is 3/4 and that Bob plays football is 2/5. What is the probability that both play football?
Medium- A3/10
- B6/20
- C1/2
- D3/5
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