Grade 10 Maths · Probability

Use the addition rule

Use P(A or B) = P(A) + P(B) − P(A and B), for example 0,5 + 0,4 − 0,2 = 0,7, and check whether events are mutually exclusive.

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Gr 11 Probability: Probability A or BKevinmathscience

Gr 11 Probability: Complimentary, mutually inclusiveKevinmathscience

Multiplication & Addition Rule - Probability - Mutually Exclusive & Independent EventsThe Organic Chemistry Tutor

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Question 10.1 · May/June 2025 · Paper 1 · National (DBE) · 2 marks

10.1 A and B are mutually exclusive events. If

P (A) = 0, 42

and

P (A or B) = 0, 79

, calculate

P (B)

.(2)

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More past paper questions: use the addition rule

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3. Question 8.2 · November 2024 · Paper 1 · Provincial · 2 marks
Consider events A and B. $P (A) = 0, 43$ , $P (B) = 0, 37$ and $P (A and B) = 0, 1591$ .
8.2 Are events A and B mutually exclusive? Explain your answer.(2)
Show the memo (2 ticks)Memo
1. ✓
  Check intersection $P (A and B) = 0, 1591 \neq = 0$
  1 mark · Use the addition rule
2. ✓
  ConclusionNot mutually exclusive because the intersection is not zero.
  1 mark · Use the addition rule
4. Question 9.3 · November 2024 · Paper 1 · Provincial · 3 marks
Two different events, A and B, forms part of an investigation. $P (A) = \frac{2}{3}$ , $P (B^{'}) = \frac{3}{5}$ , $P (A or B) = \frac{4}{7}$ .
9.3 Determine the value of $P (A and B)$ .(3)
Show the memo (3 ticks)Memo
1. ✓
  Apply Addition Rule Formula $P (A or B) = P (A) + P (B) - P (A and B)$
  1 mark · Use the addition rule
2. ✓
  Substitute values $\frac{4}{7} = \frac{2}{3} + \frac{2}{5} - P (A and B)$
  1 mark · Use the addition rule
3. ✓
  Solve for intersection $P (A and B) = \frac{52}{105}$
  1 mark · Use the addition rule
5. Question 3.1.2 · September 2024 · Provincial · 2 marks
3.1 Given: $P (A) = 0, 4$ ; $P (B) = 0, 5$ and $P (A and B) = 0, 25$ . Determine the:
3.1.2 $P (A or B)$ (2)
Show the memo (2 ticks)Memo
1. ✓
  Formula $P (A or B) = P (A) + P (B) - P (A and B) = 0, 4 + 0, 5 - 0, 25$
  1 mark · Use the addition rule
2. ✓
  Answer $= 0, 65$
  1 mark · Use the addition rule
6. Question 11.1 · September 2024 · Paper 1 · Provincial · 2 marks
Let A and B be two events in a sample space. Suppose that $P (A) = 0, 4$ $P (A or B) = 0, 7$ and $P (B) = k$ .
11.1 For what value of k are A and B mutually exclusive?(2)
Show the memo (2 ticks)Memo
1. ✓
  Substitute $0, 7 = 0, 4 + k$
  1 mark · Use the addition rule
2. ✓
  Answer $k = 0, 3$
  1 mark · Use the addition rule

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