1. The problem asks if letters and numbers can repeat in a given context. 2. To answer this, we need to understand the concept of repetition in combinatorics or arrangements. 3. If letters and numbers cannot repeat, it means each character or digit can only be used once. 4. This rule affects how many unique combinations or permutations can be formed. 5. For example, if you have 3 letters and 3 numbers, and no repetition is allowed, you can only use each letter and number once. 6. The total number of arrangements without repetition is calculated using permutations: $$P(n, r) = \frac{n!}{(n-r)!}$$ where $n$ is the total number of items and $r$ is the number chosen. 7. If repetition were allowed, the number of arrangements would be $n^r$. 8. Therefore, the answer to the question is: No, letters and numbers cannot repeat if the rule states so, which limits the number of possible arrangements.