A and Bare the only two outcomes of an event. If P(A) = 0.72, then what will be the probability of event B?

Options

A. 0.25
B. 0.28
C. 0.18
D. 0.15

Answer

To solve the problem, we need to find the probability of event B given that the probability of event A is 0.72. Since A and B are the only two outcomes of the event, we can use the fundamental rule of probability which states that the sum of the probabilities of all possible outcomes must equal 1.

### Step-by-step Solution:

1. **Understand the Given Information**:
- We know that P(A) = 0.72.
- There are only two outcomes: A and B.

2. **Use the Probability Rule**:
- According to the rule of probability, the sum of the probabilities of all outcomes must equal 1. Therefore, we can write:
\[ P(A) + P(B) = 1 \]

3. **Substitute the Known Value**:
- We can substitute the value of P(A) into the equation:
\[ 0.72 + P(B) = 1 \]

4. **Solve for P(B)**:
- To find P(B), we can rearrange the equation:
\[ P(B) = 1 - P(A) \]
- Substitute P(A) into the equation:
\[ P(B) = 1 - 0.72 \]

5. **Calculate the Result**:
- Perform the subtraction:
\[ P(B) = 0.28 \]

### Final Answer:
The probability of event B, P(B), is **0.28**.

---