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Mathematical Methods Β· Unit 1 Β· Probability Β· Conditional probability and independence

Use the notation 𝑃(𝐴|𝐡) and the formula 𝑃(𝐴 ∩ 𝐡) = 𝑃(𝐴|𝐡)𝑃(𝐡) to solve problems.

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Question 1

Refer to the scenario below. A wildlife ranger is tracking the nesting behaviour of a coastal bird species. Based on historical data: β€’ 65% of nests are located in dense vegetation (event V) β€’ When a nest is in dense vegetation, there is an 82% chance it contains three or more eggs (event E) β€’ When a nest is not in dense vegetation, there is a 45% chance it contains three or more eggs Using the conditional probability formula, calculate the probability that a randomly selected nest is both in dense vegetation and contains three or more eggs. Express your answer as a decimal correct to three decimal places.

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Question 2

A manufacturing plant produces electronic components. Quality inspectors test components in two stages: Stage 1 checks for physical defects, and Stage 2 checks for electrical faults. From historical records, the probability that a component passes Stage 1 is $0.92$. Given that a component passes Stage 1, the probability it also passes Stage 2 is $0.88$. (a) Find the probability that a randomly selected component passes both stages. (1 mark) (b) Find the probability that a randomly selected component fails at least one stage. (2 marks)

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Question 3

A medical clinic records patient test results for two screening tests. The table shows the probabilities for Test A and Test B. Determine the probability that a randomly selected patient tests positive on both tests.

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More in Conditional probability and independence

← Previous
Use the formula 𝑃(𝐴 ∩ 𝐡) = 𝑃(𝐴)𝑃(𝐡) for independent events 𝐴 and 𝐡.
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Use the rules 𝑃(𝐴) = 1 βˆ’ 𝑃(𝐴) and 𝑃(𝐴 βˆͺ 𝐡) = 𝑃(𝐴) + 𝑃(𝐡) βˆ’ 𝑃(𝐴 ∩ 𝐡).
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