Answer
The sample space is 2^{24} =16, 777,216.
Work Step by Step
From the problem, the 24 websites are classified into two; containing banner ads (denoted by C) and Not-containing banner ads (denoted by N).
The sample space of this random experiment is made up of 24 length ordered sequence of N and C.
For instance an ordered sequence of 20 Ns and 4 Cs (NNNNNNNNNNNNNNNNNNNNCCCC) or 19 Ns and 5 Cs (NNNNNNNNNNNNNNNNNNNCCCCC) and so on.
Therefore, the sample space has 224 =16, 777,216 outcomes. i.e.
