In the Scottish village Glenwhisky there are many pubs. Half of the pubs serve Dalwhinnie, and a third serve Laphroig. Only 5% of the pubs serve both Dalwhinnie and Laphroig.

(a) Angus MacAbstainer drinks only these two brands of whisky, and is otherwise a teetotaler. What is the proportion of pubs that serve at least one whisky that Angues drinks?

(b) Call the set of pubs serving Dalwhinnie, D, and the ones serving Laphroig L. For a set of pubs, A, let p(A) be the proportion of pubs that are A. Write your calculation of Angus’s pubs as a statement about the relation between p(D), p(L), P(D ∪ L), and p(DL).