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S2 binomial distribution help

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    In Joes cafe 70% of customers buy a cup of tea.
    (Can do a) a. In a random sample of 20 customers find the probability that more than 15 buy a cup of tea.

    The proportion of customers who buy a choc muffin at joes cafe is 0.35
    b. Find the probability that Joe sells the first chocolate muffin to his 5th customer/

    The probability of a customer not buying a muffin is 0.75. Think of it as a probability tree, with each branch having 2 branches at the end - one for buying a muffin, one for not buying one.

    So the probability of the 5th customer buying the first muffin would be (0.75)*(0.75)*(0.75)*(0.75)*(0.3 5) or (0.75)^4 * (0.35)
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