Provide an estimate of Facebook's annual advertising revenue.

The interviewer is requesting that you provide an estimate of Facebook's annual advertising revenue. It's crucial to understand that you aren't required to have the precise numbers; rather, this exercise evaluates your logical reasoning and capacity for making sensible estimates. Here are the main factors to consider when formulating your response: The scale of Facebook's user base: Having an approximate figure for Facebook's monthly active users will assist you in refining your estimation. The average revenue per user (ARPU): You can gauge this figure based on your assumptions about how much advertisers might be inclined to pay for each user. The frequency of ad displays: This includes any knowledge you may possess regarding Facebook’s advertising algorithm, such as how often ads appear to users on the platform.

To estimate Facebook's annual ad revenue, we can look at its number of monthly active users and the ad revenue generated per user. Currently, Facebook has around 2.6 billion monthly active users globally. If we conservatively assume that Facebook earns $10 in ad revenue per user each year, then the company's annual ad revenue would be roughly $26 billion.

There are multiple approaches to estimating Facebook's annual ad revenue, but a simple method is to consider the average revenue per user (ARPU). If we take a conservative estimate of $5 in ad revenue per user each month, and account for roughly 2.6 billion monthly active users, we can determine the yearly ad revenue to be: $5/user/month x 12 months x 2.6 billion users = $156 billion annually. It's important to note that ad revenue can fluctuate significantly based on various regions and seasonal factors, so this should be regarded as an estimation.