You started with an original solution that has a concentration of 64×10^9 bacteria per ml. You first performed three 1 to 2 dilution (500 ul of the initial solution in 500 ul of medium). Then four 1 to 100 dilutions (10 ul of the solution in 990ul of medium). You then plate 100 ul of your last dilution on a plate. How many colony forming units do you expect to see on the plate after growth?

You have a solution of bacteria. You make three 1 to 100 dilutions followed by two 1 to 10 dilutions and plate 100 ul of this solution. After 24 hours you count 47 bacteria. How many bacteria/ml did you have in the original solution and how precise do you think your number is?