What is the appropriate method for this?

In this exercise you were browsing through a refrigerator in a microbiology lab and you found a tube with a solution labeled “B. subtilis: 2 x 108 cfu/ml”. Now being the skeptic professional that you are, you want to double check the accuracy of the concentration of this culture. Describe how you would embark on this mission, how would you set up the dilutions, which plates would you chose specifically (since you are already given a specific concentration of culture), etc. The procedure in this exercise is equally important as the actual determination of the number of cfus.