Atechnician performs a serial dilution and subsequently plates the dilutions via spread plate technique. four serial 100-fold dilutions were performed, and each dilution plated. the first two plates of this series yielded too many colonies to count. the third and fourth plates yielded 255 and 3 colonies, respectively. what is the concentration of cells in the original culture? hint: the last plate should not be considered because it has too few cells for good statistical power)