title: Is it possible to estimate the average visitor duration given data for amount of exits/entries?
body: <p>I've made some software for someone to keep track of how many people are currently inside an attraction. When someone enters or leaves, I get an entry in my database marking this event. Without keeping track of individuals, is it possible to estimate the average visitor duration to this attraction with just the data I have?</p>
  
  <p>An example portion of the data I have spanning five minutes between 12:00 and 12:05 looks like this:</p>
  
  <pre><code>+----------+-----+-----+
  | Time     | In  | Out |
  +----------+-----+-----+
  | 12:00:00 |   1 |   0 |
  | 12:01:04 |   0 |   1 |
  | 12:01:05 |   0 |   1 |
  | 12:01:05 |   0 |   1 |
  | 12:01:06 |   0 |   1 |
  | 12:01:13 |   1 |   0 |
  | 12:01:13 |   1 |   0 |
  | 12:01:14 |   1 |   0 |
  | 12:01:14 |   1 |   0 |
  | 12:02:56 |   0 |   1 |
  | 12:02:56 |   0 |   1 |
  | 12:02:56 |   0 |   1 |
  | 12:02:56 |   0 |   1 |
  | 12:04:13 |   1 |   0 |
  | 12:04:13 |   1 |   0 |
  | 12:04:14 |   1 |   0 |
  | 12:04:14 |   1 |   0 |
  +----------+-----+-----+
  </code></pre>
  
  <p>At the start of the day there are no people in the attraction, so the above data is enough to calculate how many people are inside at a given time. Is there also enough information to estimate how long inside the average visitor spends?</p>