Not a riddle. Not a puzzle. Just how do you say it?
(Thanks to Doctor T for this one).

If 60% of students say they would do X and 90% say they would do Y, how much more likely are they to do Y than X. 50% more likely (i.e. 60 + 30, half again)? 33% more likely (i.e. 90-60 = 30, a third of 90)? or 150% more likely (90 = 60+half again)?

This question has upset some of the finest minds of at least one generation so far.