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June 21st, 2018, 07:02 PM   #11
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Quote:
Originally Posted by Devans99 View Post
- the murderer had blood on his clothes. Makes him 70% likely to be the killer
- the murderers prints are on the knife. Makes him 90% likely to be the killer
Change the order:
- the murderers prints are on the knife. Makes him ?% likely to be the killer
- the murderer had blood on his clothes. Makes him ?% likely to be the killer

Last edited by skipjack; June 21st, 2018 at 08:40 PM.
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June 21st, 2018, 07:12 PM   #12
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The order does not matter the answer comes out the same:

90% + 10% x 70% = 97% chance guilty
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June 21st, 2018, 09:02 PM   #13
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Some of your terms are undefined. Also, you initially used the past tense, but then switched to using present tense for no reason. Can you make a simpler example based on rolling a die, say, and give the justification for each step?
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June 22nd, 2018, 02:58 AM   #14
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It’s hard to give a die example. To state the general method I’m using:

Proposition A is x% likely because of fact 1
Proposition A is y% likely because of fact 2
How likely is proposition A taking into account fact 1 and fact 2?
x% + (100% - x%) x y%

So a simple example:
Proposition A - ‘the dog is happy’.

Fact 1 - A dog psychologist tells you 60% dogs are happy
Fact 2 - The dog is wagging his tail (80% dogs happy if wagging tail)
60% + 40% x 80% = 92%
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June 22nd, 2018, 10:21 AM   #15
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There are 100 dogs.
60 (60%) are happy.

If a dog wags tail: 80% chance it's happy.
To be happy, must be a dog from the 60 that are happy.
60*.80 = 48

So if Rin-Tin-Tin wags tail, there's a 48% chance he's happy.
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June 22nd, 2018, 10:37 AM   #16
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Quote:
Originally Posted by Denis View Post
There are 100 dogs.
60 (60%) are happy.

If a dog wags tail: 80% chance it's happy.
To be happy, must be a dog from the 60 that are happy.
60*.80 = 48

So if Rin-Tin-Tin wags tail, there's a 48% chance he's happy.
You have answered a slightly different question to what I asked: the dog does not have to be HAPPY AND WAGGING its tail, I just asked if the dog is happy.

The answer must be at least 80% because the dog is wagging his tail...
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June 22nd, 2018, 10:57 AM   #17
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See ya later buddy....this is kinda too confusing!!
I don't have a damn dog anyway
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June 22nd, 2018, 12:34 PM   #18
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OK I found the error I’m making. Thanks for all the help!
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June 22nd, 2018, 01:32 PM   #19
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Please share it with us; may help another student...
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June 24th, 2018, 02:14 PM   #20
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Revised calculation below.

Proposition 1 - There was a creator god

Big Bang is evidence for creator at 60%

Fine tuning is evidence for the creator 75% probability so:

60% + 40% x 75% = 90%

Prime mover is evidence for the creator 25% probability so:

90% + 10% x 25% = 92.5% chance of a creator god is

To double check, I’ve done the inverse proposition below:

Proposition 2 - there was not a creator

Big Bang is evidence against no creator 40%

Fine tuning is evidence against no creator 25% probability so:

40% x 25% = 10%

Prime mover is evidence against no creator 75% probability so:

10% x 75% = 7.5% chance of no creator god

Last edited by skipjack; June 24th, 2018 at 02:54 PM.
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