Human beings tend not to be very good at reasoning logically. It doesn't come naturally to us. We make mistakes. Perhaps, though, you think that you're the exception, a veritable cross between Garry Kasparov and Mr Spock (and not in the sense of being a Russian chess player with big ears). If so, let's see how you get on with this most simple of logic tests. If you can't get this right, then... well maybe you're more a right rather than left brain hemisphere kind of person...*
Here's quite a lot about Mary
There are four statements about Mary below. Your job is to rank how likely each statement is to be true in relation to the other statements (so, for example, if you think it is more likely that Mary is an executive for a housing charity than a bank clerk, you'd rate this as being more likely on the scale). A value of 1 is most likely; 4 is least likely. You have to give a different ranking for each of the four possibilities.
Mary is an executive for a housing charity
Mary is a bank clerk
Mary is an insurance salesperson
Mary is a bank clerk and remains active in the feminist movement