=+13.55 ● In a study of bacterial concentration in surface and subsurface water (“Pb and Bacteria in a Surface Microlayer” Journal of Marine Research [1982]: 1200–

1206), the accompanying data were obtained.

Concentration (3 106

/mL)

Surface 48.6 24.3 15.9 8.29 5.75 Subsurface 5.46 6.89 3.38 3.72 3.12 Surface 10.8 4.71 8.26 9.41 Subsurface 3.39 4.17 4.06 5.16 Summary quantities are