Hint:
For any random number divided by 23 has finite number of remainders.
The group of remainders modulus 23:
{0,1,2,3,4,5,6,7,...,19,20,21,22}
Since the sample space is infinite, answering this question in a rigorous way is less trivial than meets the eye.
However, it's probably meant to be answered in a trivial way, in which case you have already been given a good hint.
Out of every 23 consecutive positive integers, one of them is evenly divisible by 23, one produces a remainder of 1, one produces a remainder of 2, . . . . . , one produces a remainder of 22. So you could argue that the probability that a random integer will produce a remainder of 13 is ...... (where ...... means insert your answer here).