Opportunity samples (a convenient block of 9 squares chosen)
The first sample could only come from the second population:
The second sample must come from the third population:
Therefore the third sample must have come from the first population:
Systematic samples (every 11th square chosen)
Random samples (9 squares chosen at random)
It is possible that each sample came from any population, but more likely that the samples with more blue squares came from the populations with more blue squares. This is where they actually came from: