Mathematics for IGCSE & O level - Probability (Section 7 - No. 9)
What is the relationship between the complement of an event and the event itself?
They are the same event.
They have the same probability.
Their probabilities sum to 1.
They are mutually exclusive.
Forklaring
The complement covers everything that the event doesn't. The probabilities add to 1. They can't occur simultaneously.