You have a culture of yeast that is at a density of 4.76 x 106 cells/ml.?

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skygon13

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You dilute the sample 1:100, and then 1:100 again, and finally you dilute the sample an additional 1:3. You add 0.5 ml of the final dilution to a plate. Assuming that most of the cells in the original culture were living, how many colony-forming units do you expect to count on your plate the next day?
 
Remember that 1:X means one part culture to X parts diluent, giving you X+1 parts. This means that for 1:100 you divide by 101 which is close to 100. For 1:3, however, you must divide by 4 (1+3). This will result in a significant error.

4.76 x 10^6 cells/mL (1:100 dilution means divide by 1.01^2)
4.71 x 10^4 cells/mL (another 1:100 dilution)
4.66 x 10^2 or 466 cells/mL

466 cells/mL (1:3 dilution means divide by 4)
117 cells/mL

117cells/mL x 0.5mL = 59 cells = 59 cfu
 
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