Past exam of the mathematics course of the University of Cambridge / 2006 / iii / Paper 45 / 1 / e / Solution

In the unrearranged likelihood there are four summands. Each is a product of four supplied probabilities and takes three multiplications. Summing the four results takes three additions. ThusThis count concerns direct evaluation without reusing repeated factors; zero-or-one phenotype values could of course allow extra special-case savings.