Essential Genetics 6th Edition by Daniel Hartl

Exercise 5

A suspension of E. coli was serially diluted through two dilutions of 100-fold each and two dilutions of 10-fold each. From the final dilution, a volume of 0.1 ml was spread over nutrient agar in a petri dish and incubated overnight. The next day, 42 colonies were visible. Estimate the number of viable bacteria per milliliter in the original undiluted suspension.