Which of the following number cannot be a probability of an event?

Question

Accepted Answer

Option 2, which is -1.5, is the correct answer because it cannot be a probability of an event. Probabilities are defined as numbers that represent the likelihood of an event occurring, and they must always be within the range of 0 to 1, inclusive. This means that a probability cannot be negative or greater than 1.

1. Explanation for Option 2:
   - A probability value must be between 0 and 1. A negative number, such as -1.5, does not fit within this range. Therefore, -1.5 cannot represent a probability, as probabilities cannot be negative. This makes Option 2 the correct choice.

2. Explanation for why other options are incorrect:
   - Option 1: $\frac{2}{3}$ is approximately 0.6667, which is a valid probability value because it lies between 0 and 1. Therefore, it can be a probability of an event.
   - Option 3: 0.15 is a valid probability value because it is greater than 0 and less than 1. Thus, it can be a probability of an event.
   - Option 4: 0.7 is also a valid probability value because it is within the range of 0 to 1. Therefore, it can be a probability of an event.

In conclusion, Option 2 is the only option that cannot be a probability of an event because it is a negative number, which is outside the permissible range for probabilities.