Lesson M2

M2 Conditional probability Quiz: AQA Maths, Unit 11

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson M2, Conditional probability: 20 multiple choice questions for the AQA Maths (7357), Unit 11: Statistics, written with Revision Ninja.

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The 20 questions

  1. Which formula defines conditional probability P(A|B)?

    • P(A or B) / P(B)
    • P(A) / P(B)
    • P(A and B) x P(B)
    • P(A and B) / P(B)

  2. Events A and B are independent. What is P(A|B)?

    • P(A)
    • 0
    • P(B)
    • P(A) x P(B)

  3. In a two-stage tree diagram, what do the probabilities on the second set of branches represent?

    • Joint probabilities of both outcomes
    • Sums of all first-stage probabilities
    • Conditional probabilities given the outcome of the first stage
    • Unconditional probabilities of the second event alone

  4. In a tree diagram, how is the probability of a particular two-stage path found?

    • Multiply the probabilities along its branches
    • Add the probabilities along its branches
    • Divide the first branch probability by the second
    • Take the larger of the two branch probabilities

  5. Which statement about the probabilities on the branches leaving one node of a tree diagram is correct?

    • They each equal 0.5
    • They multiply to give 1
    • They sum to 1
    • They sum to 0

  6. Which formula gives P(A and B) when P(B) and P(A|B) are known?

    • P(B) x P(A|B)
    • P(B) + P(A|B)
    • P(B) - P(A|B)
    • P(A|B) / P(B)

  7. P(A) = 0.4, P(B) = 0.5 and P(A and B) = 0.1. What is P(A|B)?

    • 0.04
    • 0.8
    • 0.2
    • 0.25

  8. P(A) = 0.6 and P(B|A) = 0.3. What is P(A and B)?

    • 0.18
    • 0.90
    • 0.30
    • 0.50

  9. In a class of 30 students, 12 study Chemistry. Of these 12, 4 also study Physics. A student is chosen at random from those who study Chemistry. What is the probability they also study Physics?

    • 1/8
    • 4/30
    • 2/5
    • 1/3

  10. A group has 30 members and 20 non-members. 18 members and 8 non-members buy online. Given a person bought online, what is the probability they are a member?

    • 18/50
    • 26/30
    • 18/30
    • 9/13

  11. P(A) = 0.5 and P(B) = 0.8, with P(A|B) = 0.5. Which statement is correct?

    • A and B are independent since P(A|B) = P(A)
    • A and B are mutually exclusive since P(A and B) is zero
    • A and B are independent since P(B) is greater than P(A)
    • A and B are not independent since P(A) + P(B) is greater than 1

  12. A bag holds 3 red and 2 blue balls. Two balls are drawn without replacement. What is the probability both are red?

    • 9/25
    • 1/4
    • 3/10
    • 2/5

  13. The same bag holds 3 red and 2 blue balls. Two balls are drawn without replacement. What is the probability the second ball is blue?

    • 2/5
    • 1/2
    • 3/5
    • 1/5

  14. P(A) = 0.3, P(B) = 0.5 and P(A or B) = 0.6. What is P(A|B)?

    • 0.4
    • 0.12
    • 0.2
    • 0.6

  15. P(A|B) = 0.7, P(B) = 0.2 and P(A|B') = 0.1. What is P(A)?

    • 0.16
    • 0.22
    • 0.08
    • 0.14

  16. A factory makes 60% of items on machine X, with a 2% defect rate, and 40% on machine Y, with a 5% defect rate. What is the probability an item came from X given it is defective?

    • 5/8
    • 0.012
    • 3/5
    • 3/8

  17. A disease affects 1% of people. A test is positive for 90% of affected people and 5% of unaffected people. What is the probability a person with a positive test has the disease?

    • approximately 0.010
    • approximately 0.500
    • approximately 0.900
    • approximately 0.154

  18. P(A) = 0.4, P(B) = 0.5 and P(A and B) = 0.2. Which statement is correct?

    • They are independent since P(A and B) = P(A) x P(B)
    • They are not independent since P(A|B) = 0.2
    • They are mutually exclusive since P(A and B) is positive
    • They are not independent since P(B|A) = 0.5

  19. P(A) = 0.2, P(B|A) = 0.6 and P(B|A') = 0.3. What is P(A'|B)?

    • 3/5
    • 2/3
    • 0.24
    • 1/3

  20. A card is drawn from a standard 52-card pack. Given that it is red, what is the probability it is a heart?

    • 1/4
    • 1/2
    • 1/13
    • 13/52

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