Compound events, the addition rule and mutual exclusivity
A synthetic classification records two properties for each message
Event A: the message is unread. Event B: the message has an attachment
Let S be the sample space of all 18 recorded cases
The counts in the four disjoint regions are shown below
| Region | Count |
|---|---|
| A only | 6 |
| B only | 9 |
| A and B | 0 |
| Neither A nor B | 3 |
For the requested probability, select one recorded case uniformly at random