Going on from the lively discussions on how likely certain parasites are to be affecting certain fondly viewed silvery tourists here's another festive brain teaser:

There is a disease that affects 1 in 10,000 fish that makes them unsuitable for human consumption. An angler has caught a fish and taken two fillets - one of which she eats and one which she freezes. The next day, she gets a call from a health inspector who is testing all fish taken home from her local fishery for this disease. The health inspector has a test for the frozen fillet that can tell with 99% accuracy whether the fish she has eaten had the disease.

A week later the result comes back as positive, would you be worried? What is the probability that the angler has eaten diseased fish?

I assume 100% as both fillets are from the one fish??

(I can see now (19/12) that I completely misread the question ---- doh!)

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Cheers
Don

Doesn't really matter.... she's already croaked.

The probability is 99/100 or, a 99% chance...... isn't it?

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Too much Saturn, not enough Moon.

Buzzers 2012


Fly Clips & Stands

Well Walty and Scratch,

I can tell you that around 70% of the current voted answers are wrong so far!

Right, you've lost me already. Bye

__________________
Too much Saturn, not enough Moon.

Buzzers 2012


Fly Clips & Stands

For the people who got the correct answer......can you show your working to the rest of the class plz

I still believe I was right with 99/100 Paul....

If the test is 99% accurate, then that means that for every 100 fish tested, 99 of the results will be correct.

__________________
Too much Saturn, not enough Moon.

Buzzers 2012


Fly Clips & Stands

.....by the same token it means that 1 in 100 will be wrong.

edit to clarify; "wrong" would include "False Positive", which is a better clue.

Such subterfuge; 'smoke & mirrors'.

Paul perhaps you shouldn't have made the poll anonymous; more fun knowing who voted for what.


Wrong or not I voted 99/100.





As for "certain fondly viewed silvery tourists" I'm sure that you also meant to include "critically endangered large spring salmon" knowing that that 3+SW group on the Wye has declined by 99% in, say, the 30 years compared to only 90% of the "threatened" 2SW group?

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Save the softmouth trout

Assuming that the incidence is accurate, 1 in 10,000 translates to a 0.01% chance of getting the disease. The precision level of the test is 1%, which means that the chance of getting a false positive is 100 times more than the chance of catching the disease.

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Nos du, nos da