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S2 Poisson Distribution question

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    • Thread Starter

    The question is
    'The number of breakdowns per day of the lifts in a large block of flats is modelled by a Poisson distribution with mean 0.2.
    a) Find the probability that on a particular day there will be at least one breakdown.
    b) Find the probability there are fewer than two days in a 30 day month with at least one breakdown.'
    I managed part a fine and got the right answer (0.181 to 3 d.p.)
    I'm stuck on part b though. I've tried using the binomial distribution formula because I thought there were a fixed number of trials (30) and a constant probability. I worked out the probability for one or zero days with at least one break down and added them but I got the wrong answer.....
    I'm not sure what I'm doing wrong.

    What did you get as the answer to part (b) ?
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