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machine components

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by mehrasa » Wed Sep 28, 2011 12:09 am
a machine is made up of to components, A and B. Each components either work or fail.. their failure and non failure of these components are independent. the machine work if at least one of the components works. if the probability that each component work is 2/3. what is the probability that the machine works?
1/9
4/9
1/2
2/3
8/9
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by shankar.ashwin » Wed Sep 28, 2011 12:19 am
Prob of component working = 2/3

Therefore, Prob of failure = 1/3

Now machine will work if atleast one of the components work;

P(atleast one component works) = 1 - P(Both comp. fails)

= 1 - (1/3)(1/3)

= 8/9
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by chetansharma » Wed Sep 28, 2011 12:20 am
IMO the answer is E

Calculate for the negative cases and remove from 1. Each component has a probability of 1/3 in not to work.
For the entire machine to stop working both A AND B components should not work.

SO the required probability is 1-(1/3*1/3) = [spoiler]8/9[/spoiler]

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Chetan
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