A crime has occured in Carborough, involving a taxi. The police interviewed an eyewitness, who stated that the taxi involved was blue.

The police know that 85% of taxis in Carborough are blue, the other 15% being green. They also know that statistically witnesses in these situations tend to be correct 80% of the time - which means they report things wrong the other 20% of the time.

What is the probability that the taxi involved in the crime was actually blue?

(In reply to A more paradoxical version. by Charlie)

I thought simple arithmetic errors was my job?!?

17+12 is usually 29, rather than 39 - which makes the final percentage for green taxis ~41.4%

What it does show is that irrespective of what the witness said the police should investigate blue taxis.

Posted by fwaff on 2003-03-27 06:30:37