The rule of sum in discrete
mathematics is a way to count a set of objects into independent elements. The
rule of sum presents an idea that if one situation can occur in \(A\) ways and
another situation can occur in \(B\) ways, then there are \(A+B\) ways that one of
these types of situations may occur.
For example, a restaurant
serves fifteen entrees that contain meat, five entrees that contain fish and
three vegetarian entrees. How many dinners are there to choose from?
The rule of sum is applied
here because each entrée contains either meat or fish or is vegetarian. So we
have \(15+5+3=23.\)