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2.3.3 Conditional probability (A-level only)

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Question 74

A pharmaceutical research company is testing the effectiveness of a new antiviral treatment, therapy TTT. In a clinical trial involving a large cohort of patients, two events were recorded:

Event T T\,T is defined as the patient receiving the antiviral therapy.

Event R R\,R is defined as the patient showing a significant reduction in viral load within 24 hours.

The following table summarises the joint probabilities for these events based on the trial data:

RRRR′R'R′
TTT0.360.24
T′T'T′0.120.28
a.

A patient from the trial is selected at random.

(i) Find P(T)P(T)P(T).

(ii) Find P((T∩R)′)P((T \cap R)')P((T∩R)′).

(iii) Find P(R∣T′)P(R | T')P(R∣T′).

[4]
b.

Determine whether the events T T\,T and R R\,R are independent. Fully justify your answer.

[3]

2.3.3 Conditional probability (A-level only) Questions

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