Complete and use a two-way probability table

A set of paper samples is classified by two binary properties

Event A means an item has a square mark; event B means an item is folded once. The sample space is S, and the complements are A′ and B′

Event B is shown in the rows and event A is shown in the columns. Not A and Not B denote the complementary categories. The entries are counts of items

One item is selected uniformly at random from these recorded items