Probability: theoretical probability — KCSE Mathematics

KCSE Mathematics · 99 practice questions · 3 syllabus objectives

35 easy34 medium30 hard

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Define the sample space, event and probability; calculate P(E) = n(favourable outcomes)/n(sample space) for equally likely outcomes

Apply the complementary rule P(E') = 1 – P(E) and identify mutually exclusive and independent events

Probability: theoretical probability

Sample Questions

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1
easySHORT ANSWER3 marks

State whether the events of flipping a coin and rolling a die are independent. Justify your answer. (3 marks)

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Part (a) — 1 mark
The events are independent. (1 mk)
Part (b) — 2 marks
The outcome of flipping a coin does not affect the outcome of rolling a die. (1 mk)
Mathematically, P(A and B) = P(A) * P(B) for independent events. (1 mk)
2
easySHORT ANSWER2 marks

State the probability of not rolling a six when a fair die is thrown once. (2 marks)

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Part (a) — 2 marks
P(not rolling a six) = 1 - P(rolling a six) (1 mk)
P(rolling a six) = 1/6, thus P(not rolling a six) = 5/6 (1 mk)
3
easySHORT ANSWER4 marks

A spinner is divided into 8 equal sections numbered from 1 to 8. (a) Describe the sample space when the spinner is spun once. (2 marks) (b) Find the probability of landing on an even number. (2 marks)

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Part (a) — 2 marks
Sample space: {1, 2, 3, 4, 5, 6, 7, 8} (1 mk)
Total outcomes = 8 (1 mk)
Part (b) — 2 marks
Favourable outcomes = 4 (Even numbers: 2, 4, 6, 8) (1 mk)
P(Even) = 4/8 = 1/2 (1 mk)
4

A bag contains 5 red marbles, 3 blue marbles, and 2 green marbles. (a) State the sample space when one marble is drawn. (2 marks) (b) Calculate the probability of drawing a blue marble. (2 marks)

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