Hi there, I'm not sure if this question is WITH replacement or WITHOUT replacement. I tried it both ways and didn't come to the correct answer. I'm assuming this question makes more sense WITHOUT replacement.

Question:

http://i.imgur.com/nfBSA.png

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- Jul 6th 2011, 08:48 PMMathsBeforeBedtimeProbability using tree diagrams
Hi there, I'm not sure if this question is WITH replacement or WITHOUT replacement. I tried it both ways and didn't come to the correct answer. I'm assuming this question makes more sense WITHOUT replacement.

Question:

http://i.imgur.com/nfBSA.png - Jul 7th 2011, 02:44 AMe^(i*pi)Re: Probability using tree diagrams
Without replacement makes more sense to me, why would you replace a car that is known (not) to work?

What have you tried as to solving the question?

On a tree diagram you*multiply along*the branches and*add down*the branches. - Jul 7th 2011, 03:28 AMMathsBeforeBedtimeRe: Probability using tree diagrams
Yes I know this. I did Faulty and not faulty.

{Faulty = 3 / 100 Not Faulty = 97/100} - first branch

{(Faulty = 2 / 99 and Not Faulty = 97/99) comes off the Faulty branch, (Faulty = 3 / 99, Not Faulty = 96 / 99) comes off the not faulty branch} - Second branch

{(Faulty = 1 / 98 and Not Faulty = 97/98) comes off the first Faulty branch and second faulty branch...Etc Think you'll understand what I mean} - Third branch

I did P(1 is faulty) = (3/100*97/98*96/98) + (97/100*3/99*96/98) + (97/100*96/99*3/98) = 1164 / 13475

Correct answer: 84 681 / 1 000 000 - Jul 7th 2011, 03:48 AMmr fantasticRe: Probability using tree diagrams
- Jul 9th 2011, 04:41 AMMathsBeforeBedtimeRe: Probability using tree diagrams
Turns out it is with replacement. P(1 is faulty)=3/100*97/100*97/100 *3 =84 681 / 1 000 000

- Jul 9th 2011, 04:24 PMmr fantasticRe: Probability using tree diagrams