Try this little test:
Imagine that you are blindfolded and there is a bag in front of you containing a large number of five different types of sweet. How many must you take out of the bag to be certain of having chosen three of the same type?
Think about it for a few minutes, it's not that hard.
Now if you got the right answer, phone up your local Primary School and offer to teach the staff.
(The answer's in this article)
Apparently only one in five new British Primary School Teachers can solve this problem, which according to their spokesperson; means that 75% can't.