When calculating the concentration of bacteria in a liquid culture, you should plate multiple dilutions of your culture then count the colonies that develop on only one of those plates.  The plate that you count should contain between 30 and 300 colonies.  Should you avoid using plates with fewer than 30 or more than 300 colonies because some error in your technique led to those numbers of colonies, or because using fewer than 30 and more than 300 colonies can lead to an error in your calculations?  Explain your answer.