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Nov 2019 p63 q7
3290
A competition is taking place between two choirs, the Notes and the Classics. There is a large audience for the competition.
30% of the audience are Notes supporters.
45% of the audience are Classics supporters.
The rest of the audience are not supporters of either of these choirs.
No one in the audience supports both of these choirs.
A random sample of 240 people is chosen from the audience. Use a suitable approximation to find the probability that fewer than 50 do not support either of the choirs.
Solution
Let the probability that a person does not support either choir be denoted by \(p\). Given that 30% support Notes and 45% support Classics, the probability of not supporting either is:
\(p = 1 - 0.30 - 0.45 = 0.25\)
The mean number of people in the sample who do not support either choir is: