Either you know it or You Don't

Either you know the subject (in which case you're absolutely certain of the outcome and know it a 100 percent) or you don't (in which case you have no business taking the examination until you've learned what you need to know to score perfect).

Negative times a Negative

A good percentage of people can't explain or understand the idea of a Negative times a Negative makes a positive. Just think about it for a second with this little anecdote.

Let's say there is a five dollar late fee on a utility bill. We're going to say that the payment is made on time, four consecutive times which is equivalent to (-4). So, all four time you avoided a five dollar fee (-5). Multiply the two together and you've saved yourself twenty dollars (+20) positive.