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The professor who sometimes forgets to bring her briefcase to the office, but assume that, each day, the probability that she forgets the briefcase is 1 /8 . Assume that her forgetting is a Bernoulli process.

(1) What is the probability that she remembers to bring her briefcase every day in one week (5 days)?

(2) What is the probability that she forgets to bring her briefcase every day in one week (5 days)?

(3) What is the probability that she forgets to bring her briefcase at least one day in one week (5 days)?

So I'm having a little trouble. The first time I tried this I did the following: 1-(5,0)*1/8^0*7/8^5 Which was incorrect. Any thoughts? Thanks in advance!

Eric
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2 Answers2

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Wow, the power of Google.

Yahoo answers

Seems like you just posted your homework with any any attempt to solve the problem.

El Santi
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  • So if you don't want to actually help why are you here? And you're right it's not like I posted the work I already tried in the question and showed that I attempted it. Oh wait.. – Eric Oct 07 '14 at 08:09
  • Sorry Eric, I just googled your question and found answer that was worked out. – El Santi Oct 07 '14 at 08:11
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$p$ = probability that she forgets to bring the briefcase, then $p = \dfrac{1}{8}$, and $q$ = probability that she remembers to bring the briefcase each day, then $q = 1 - p = \dfrac{7}{8}$. Thus:

a) $P(A) = \left(\dfrac{7}{8}\right)^5$.

b) $P(B) = \left(\dfrac{1}{8}\right)^5$.

c) $P(C) = 1 - \left(\dfrac{7}{8}\right)^5$

DeepSea
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  • Thank you very much. Looks like I was doing it backwards. Can't seem to wrap my head around this Bernoulli nonsense. – Eric Oct 07 '14 at 08:16