Maximum number of nodes connected when the link has a large buffer
You can have ten of them going at once.  If they're on a third of the time and you decree that, for instance, ten operate for twenty seconds, then the next ten, then the next ten, then you can have thirty of them total.

If you just focused on the max you'd think that you could only have ten (which would be the case if you weren't able to synchronize them, and thus couldn't rule out that they might all try to talk at once.)

By averaging over the available time you can get the same result without having to speculate about how exactly to schedule them.  Over its uptime, each node transmits at an average of 3+1/3 Mbps.  Dividing 100 MBps by this number gives 30.