Do they earn if you skip the adverts or is it solely based on views?
A number of factors affects it:
How much of the video is watched 30 secs Vs 10 minutes
How long people watch the ads (which is why quite a lot of YouTubers are starting to out 2 back to back, shorter, non-skippable ads in videos)
How many ads are in your video
The CPM at that time (higher in December because it's Christmas and so brands pay YouTube to have ads so people buy stuff, lower in January because people don't spend money in the new year)
As I said I just went with the average RPM of this other persons analytics, then used her average views stats from social blade. So she could have earned more/less in the past month. But not by loads.