Bacterial resistance to antibiotics is a concern, and bacteria may be adapt- ing to non-zero levels of antibiotics in sewage. We will take some sewage, treat it with some kind of antibiotic, grow it on a plate, and then count the bacteria that survive. Forty-eight preparations were made, three each for the combinations of origin of sample (activated sludge or effluent), growth medium (LB or CAGY), and antibiotic (Amoxicillin, Tetracycline, Tylosin,

or none). Bacterial counts (per L of sample) are in the following table (data adapted from S. Ghosh, pers. comm., data set cfcdae::SewageBacteria).

(a) Analyze these data to determine the effects of the factors on bacterial counts.

(b) There is something truly bizarre in these data; what is it?