The choice of how many slices of pizza and/or how many large pepsi is to be bought comes from the idea of which of the two products will give more satisfaction to the consumer.
It is a common knowledge that for several number of pizza,a person can only consume minimal amount of pepsi. For maximum satisfaction, a combination of 2:1 may be used. That is, for very two slices of pizza, one may buy a large pepsi costing $2.
Given that the money available is $20 then, 5 sets of 2 slices of pizza and large pepsi may be purchased.