Final answer:
The estimated concentration of cells/ml in the original broth culture is 5 million cells/mL.
Step-by-step explanation:
The estimated concentration of cells/ml in the original broth culture can be calculated by using the dilution factor and the number of colonies counted on the plates. In this case, the dilution factor is 10,000. From the 1:10,000 dilution, an average of 50 colonies was counted on the plates. Multiplying the number of colonies by the dilution factor gives us the estimated concentration of 5 million cells/mL in the original broth culture.