2. You receive a stock solution of unknown bacterial concentration and are asked to make a series of five 10-fold dilutions (dilutions #1 – #5). You then plate 100ul from each dilution and count the colonies that develop on each plate (plate #1 – #5, corresponding to the dilution used). On plate #5 you find 15 colonies. On plate #4 you find 166 colonies. Plate #3 has too many colonies to count.
A. What do you multiply the number of colonies by to get the concentration of cells in the dilution you plated from?
B. What is the concentration of bacteria in the original stock solution?
Include your concentration units. Show your work to get credit.
