Lesson 2.03d

2.03d Conditional probability Quiz: OCR Maths, Unit 13

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 2.03d, Conditional probability: 20 multiple choice questions for the OCR Maths (H240), Unit 13: Probability, written with Revision Ninja.

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The 20 questions

  1. In conditional probability notation, what does P(A | B) represent?

    • Probability of A given B
    • Probability of A or B
    • Probability of A and B
    • Probability of B given A

  2. What is the conditional probability formula for P(A | B)?

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

  3. If A and B are independent, what is P(A | B)?

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

  4. What type of probabilities do second-stage branches on a probability tree diagram represent?

    • Independent probabilities
    • Conditional probabilities
    • Joint probabilities
    • Marginal probabilities

  5. When using a contingency table for conditional probability P(A | B), what forms the restricted sample space?

    • Intersection of A and B
    • The entire table
    • Column or row for A
    • Column or row for B

  6. On a Venn diagram, how is the conditional probability P(A | B) calculated?

    • Intersection over union
    • Union over B area
    • B area over intersection
    • Intersection over B area

  7. What relationship between events A and B is defined by P(A | B) = P(A)?

    • Exhaustive
    • Dependent
    • Independent
    • Mutually exclusive

  8. A survey: 20 girls, of whom 9 said yes, and 30 boys, of whom 16 said yes. What is P(yes | girl)?

    • 9/20
    • 11/20
    • 9/25
    • 1/2

  9. In the same survey, what is P(girl | yes)?

    • 9/20
    • 9/25
    • 9/50
    • 11/25

  10. Two fair dice are rolled. Given that the first die shows 3, what is the probability that the total is 7?

    • 1/3
    • 1/6
    • 1/12
    • 1/36

  11. A bag has 3 red and 2 blue balls. Two are drawn without replacement. Given the first ball is red, what is the probability that the second is red?

    • 3/10
    • 2/5
    • 3/5
    • 1/2

  12. The same bag has 3 red and 2 blue balls. What is the probability that both balls drawn without replacement are red?

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

  13. Given P(A) = 0.4 and P(A | B) = 0.4, what relationship exists between events A and B?

    • Dependent
    • Mutually exclusive
    • Complementary
    • Independent

  14. P(A and B) = 0.12 and P(B) = 0.4. What is P(A | B)?

    • 0.08
    • 0.48
    • 0.3
    • 0.12

  15. P(A) = 0.5 and P(A and B) = 0.2. What is P(B | A)?

    • 0.7
    • 0.1
    • 0.4
    • 0.2

  16. A bag contains 4 red and 6 blue balls. Two are drawn without replacement. What is the probability that both are blue?

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

  17. The same bag has 4 red and 6 blue balls, two drawn without replacement. What is the probability that at least one is red?

    • 1/3
    • 7/10
    • 2/3
    • 3/5

  18. P(B) = 0.6 and P(A | B) = 0.25. What is P(A and B)?

    • 0.25
    • 0.15
    • 0.6
    • 0.3

  19. P(A') = 0.7, P(A and B) = 0.2 and P(B) = 0.5. What is P(A | B)?

    • 0.5
    • 0.7
    • 0.2
    • 0.4

  20. Given P(A) = 0.3 and P(A | B) = 0.5, what relationship exists between events A and B?

    • Independent
    • Mutually exclusive
    • Exhaustive
    • Dependent

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