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
| A | Not A | Total | |
|---|---|---|---|
| B | 11 | 12 | 23 |
| Not B | ? | 3 | 14 |
| Total | 22 | 15 | 37 |