33) A

Probability of getting psychosis by reasons others than cannabis = y.
Since 80% of the population do not use cannabis, probability of getting psychosis by reasons other than cannabis = 80% x y = 0.8y

20% of the population use cannabis. However, they have the same probability ‘y’ of getting psychosis plus the 41%.

This gives us the equation:

(0.41 x 0.2y) ÷ [(1.41 x 0.2y) + 0.8y] = 0.082 ÷ 1.08 ≈ 0.08/1.1

Percentage = (0.08 / 1.1) x 100 = 8%

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