Final answer:
The probability of needing to survey at most three pages to find one with a footwear ad, and the expected number of pages to survey before finding a footwear ad, involves statistics. Without specific data, we cannot precisely calculate these probabilities or expectations.
Step-by-step explanation:
The question posed is related to the probability and expectation, which are key concepts in statistics, a branch of mathematics. To determine the likelihood of needing to survey at most three pages to find one advertising footwear, you would calculate the probability based on the distribution of footwear ads across the pages. Furthermore, to find out the expected number of pages you'd need to survey before coming across an ad for footwear, you would use the concept of mathematical expectation.
As for how many pages you might expect to advertise footwear, this would also be an expectation calculation. However, to assess whether it's probable that all 20 pages will advertise footwear, you would need additional data on the proportion of pages that typically advertise footwear. Without this information, it is not possible to give a precise probability, but generally speaking, it is unlikely that all pages would feature footwear advertisements unless there's a strong predisposition towards footwear in the sampling of pages.