What is the probability of a certain event?

Options

A. 1
B. -1
C. 0
D. `1/2`

Answer

To find the probability of a certain event, we can follow these steps:

### Step-by-Step Solution:

1. **Define the Event**: A certain event is an event that is guaranteed to happen. For example, if we have a box containing only red balls, the event of drawing a red ball is certain.

2. **Identify the Favorable Outcomes**: In our example, the favorable outcomes are the red balls. If there are 5 red balls in the box, then the number of favorable outcomes is 5.

3. **Identify the Total Outcomes**: The total outcomes refer to the total number of balls in the box. In this case, since there are only red balls, the total number of outcomes is also 5.

4. **Calculate the Probability**: The probability of an event is calculated using the formula:
\[ \text{Probability} = \frac{\text{Number of Favorable Outcomes}}{\text{Total Number of Outcomes}} \]
Substituting the values we identified:
\[ \text{Probability} = \frac{5}{5} = 1 \]

5. **Conclusion**: Since the probability of a certain event is always 1, we conclude that the probability of drawing a red ball from a box containing only red balls is 1.

### Final Answer:
The probability of a certain event is **1**.

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