Problem
I. You diluted your culture 1/20 and plated 0.2ml. After incubation you had 25 colonies on the plate. What will be the original concentration of culture?
II. The concentration of overnight E.coli culture is 2.5*10^7 cfu/ml. You were asked to achieve 200 colonies with pour plate method. At some point, which of the following you will have to perform.
i. 1.0 ml of culture + 2.5 ml of buffer
ii. 1.0 ml of culture + 0.25 ml of buffer
iii. 1.0 ml of culture + 1.0 ml of buffer
iv. 1.0 ml of culture + 0.5 ml of buffer
v. 1.0 ml of culture + 1.5 ml of buffer
III. You prepared a solution by adding 2g of Nacl to 125ml of water. What will be the % by mass of this solution will be?