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The probability that a convenience store has no iced tea is

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Senior Manager
Joined: 23 May 2005
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Location: Sing/ HK
The probability that a convenience store has no iced tea is [#permalink]

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20 Nov 2006, 10:28
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The probability that a convenience store has no iced tea is 50%. If Karl is stopping by 3 convenience stores on his way to work, what is the probability that he will not be able to buy a can of iced tea?

what is the correct way of solving this?

--> (1/2)(1/2)(1/2) = 1/8

or

--> 1-(1/2)(1/2)(1/2) = 7/8

I often get confused when to use 1 - (probability of x not happening) vs just multiplying the probability that an even happens x times.

Anyone care to give their thoughts?
_________________

Impossible is nothing

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Manager
Joined: 01 Oct 2006
Posts: 240

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20 Nov 2006, 13:52
The answer will be 1/8. (Multiply the probabilities when calculating the probabilities of all the events to happen together)

7/8 is the probability that at least one of the stores has iced tea.

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Director
Joined: 28 Dec 2005
Posts: 915

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20 Nov 2006, 15:43
Agree 1/8.

Try binomial: if probability of outcome A (no iced tea) happening for each event is p=1/2.

What is the probability that in n (3) events, the outcome A (no iced tea) occurs thrice?
nCk*p^(k)*(1-p)^(n-k)

3C3* (1/2)^3 * (1/2)^0 = 1/8.

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VP
Joined: 25 Jun 2006
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20 Nov 2006, 17:51
1/2*1/2*1/2 = 1/8.

all must not have the iced tea.

Kudos [?]: 204 [0], given: 0

20 Nov 2006, 17:51
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The probability that a convenience store has no iced tea is

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