Joined: June 2004
I don't know why you are insisting on taking thing so slowly.
But OK, I happily accept that IF you know that 90% of a group have a particular property then a randomly chosen member of the group is 90% likely to have that property.
However I will point out that you have to know that 90% of the group DO have that property (or at least have a valid extrapolation that is not biased by the choice of sample). And I hope that it is not necessary to note that the argument cannot be reversed so that it is argued that an individual with the property in question is 90% likely to belong to the group.