the third floor is where the high school students are. a number of these are also canned. these rules lead to another (equivalent) rule—the sign of any product a × b depends on the sign of a as follows:
 if a is positive, then the sign of a × b is the same as the sign of b, and
 if a is negative, then the sign of a × b is the opposite of the sign of b.
the justification for why the product of two negative numbers is a positive number can be observed in the analysis of complex numbers. 