Conditional Probability Analysis for Testing Independence

00:00 7 marks

  • Build Confidence
  • SL & HL
  • Tier 3
  • Conditional Probability
  • Independence of events
  • Intersection of Events

Consider two events A and B. The probability of event A is \(P(A)=0.5\), the probability of event B is \(P(B)=0.4\), and the conditional probability of B given A is \(P(B|A)=0.6\).

(a) Find \(P(A\cap B)\).

(b) Compute \(P(A|B)\) using the result from part (a).

(c) Determine whether events A and B are independent. Justify your answer.

Part a

3 minutes 2 marks

Question

Given that \(P(B|A)=0.6\) and \(P(A)=0.5\), find \(P(A\cap B)\).



Hint Hint

Hint

Use the definition of conditional probability: \(P(B|A)=\frac{P(A\cap B)}{P(A)}\). Rearrange this formula to solve for \(P(A\cap B)\).

  • Answer Answer

Complete Answer

0.3

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Part b

2 minutes 2 marks

Question

Using your answer from part (a), compute \(P(A|B)\) given that \(P(B)=0.4\).



Hint Hint

Hint

Use the formula for conditional probability: \(P(A|B)=\frac{P(A\cap B)}{P(B)}\). Substitute the value of \(P(A\cap B)\) from part (a) and the given value of \(P(B)\).

  • Answer Answer

Complete Answer

0.75

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Part c

3 minutes 3 marks

Question

Determine whether events A and B are independent. Justify your answer using probabilities calculated in the previous parts.



Hint Hint

Hint

Events A and B are independent if and only if \(P(A\cap B) = P(A) \times P(B)\). Check if this condition holds using the given probabilities and the result from part (a). Alternatively, check if \(P(A|B) = P(A)\) or \(P(B|A) = P(B)\).

  • Answer Answer

Complete Answer

Events A and B are not independent because \(P(A\cap B) = 0.3\) and \(P(A) \times P(B) = 0.5 \times 0.4 = 0.2\). Since \(0.3
eq 0.2\), the condition for independence is not satisfied.

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