Which rule must be used to find out the number of ways that two representatives can be picked so that one is a mathematics major and the other is a computer science major?
The "product line" rule must be used to find out the number of ways that two representatives can be picked so that one is a mathematics major and the other is a computer science major.
The product line states that if the two functions f(x) and g(x) are differentiable (i.e. the derivative exist) then the product is differentiable and: