Final answer:
The number that could not be used to represent the probability of an event is -1.
Step-by-step explanation:
The number that could not be used to represent the probability of an event is d) -1.
- a) 0: This represents the probability of an impossible event, meaning it will never occur.
- b) 0.5: This represents a 50% chance or a 1 in 2 probability.
- c) 1: This represents a certain event, meaning it will always occur.
- d) -1: Negative numbers cannot be used to represent probabilities because probabilities are always non-negative.