What is the sum of all probabilities of an event.

Answer

To find the sum of all probabilities of an event, we can follow these steps:

### Step-by-Step Solution

1. **Understanding the Event**: When we talk about the sum of probabilities of an event, we need to consider all possible outcomes of that event. For example, when flipping a coin, the possible outcomes are heads (H) and tails (T).

2. **Identifying Probabilities**:
- The probability of getting heads (P(H)) is 1 out of 2 possible outcomes, which can be expressed as:
\[ P(H) = \frac{1}{2} \]
- The probability of getting tails (P(T)) is also 1 out of 2 possible outcomes, expressed as:
\[ P(T) = \frac{1}{2} \]

3. **Calculating the Sum of Probabilities**:
- To find the sum of the probabilities of all possible outcomes, we add the probabilities of heads and tails:
\[ \text{Sum of Probabilities} = P(H) + P(T) \]
- Substituting the values we found:
\[ \text{Sum of Probabilities} = \frac{1}{2} + \frac{1}{2} \]

4. **Finding a Common Denominator**:
- The least common multiple (LCM) of the denominators (which is 2) allows us to add the fractions:
\[ \text{Sum of Probabilities} = \frac{1 + 1}{2} = \frac{2}{2} \]

5. **Final Result**:
- Simplifying \(\frac{2}{2}\) gives us:
\[ \text{Sum of Probabilities} = 1 \]

### Conclusion
The sum of all probabilities of an event is always equal to 1.