The odds in favour of the occurrence of an event are `3:5`. Find the probability of the non-occurrence of the event.

Explanation

To solve the problem, we need to find the probability of the non-occurrence of an event given that the odds in favor of the occurrence of the event are 3:5.

### Step-by-Step Solution:

1. **Understanding Odds**: The odds in favor of an event are given as 3:5. This means that for every 3 favorable outcomes (occurrence of the event), there are 5 unfavorable outcomes (non-occurrence of the event).

2. **Identifying Favorable and Unfavorable Outcomes**:
- Favorable outcomes (occurrence of the event) = 3
- Unfavorable outcomes (non-occurrence of the event) = 5

3. **Calculating Total Outcomes**:
- Total outcomes = Favorable outcomes + Unfavorable outcomes
- Total outcomes = 3 + 5 = 8

4. **Finding Probability of Non-Occurrence**:
- The probability of non-occurrence of the event is given by the ratio of unfavorable outcomes to the total outcomes.
- Probability of non-occurrence = Unfavorable outcomes / Total outcomes
- Probability of non-occurrence = 5 / 8

5. **Final Answer**: Therefore, the probability of the non-occurrence of the event is \( \frac{5}{8} \).

### Summary:
The probability of the non-occurrence of the event is \( \frac{5}{8} \).