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# Need help on a basic probability question Watch

1. I missed a bunch of lessons on probability during Stats 1 at AS level and just need a hand with this question:

Each evening Aaron sets his alarm for 7am. He believes that the probability that he wakes before his alarm rings each morning is 0.4 and is independent from morning to morning.
What is the probability that, during a week (7 mornings) he wakes before his alarm:
a) on 2 or fewer mornings
b) on more than 1 but fewer then 5 mornings

Thanks.
2. In a situation where you have a fixed number of independent events, each with equal probability of occurring, you use the binomial distribution. Are you familiar with this?
3. you can work probabilities of this type out using the binomial distribution. where n is the number of independent trials and p the probability of success and x the number of successes.

x~Bin (n,p)

p(X=x) = nCx * p^(x) * (1-p)^(n-x)
4. Okay thanks. I've used binomial distribution and got the right answer, though I haven't covered it before I do understand it. Thanks again.

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Updated: April 15, 2013
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