Answers for Serial Dilution Problem # 4

1. Which is the countable plate? "A" # CFU = 250
2. What is the SDF? 1/1
3. Calculate the ITDF:
   1. 0.5 ml / 0.5 ml + 4.5 ml = 0.5 ml / 5.0 ml = 1/10
   2. See Above = 1/10
   3. See Above = 1/10
   4. See Above = 1/10
4. Calculate the TSDF for the countable plate.
   • 1/10
5. Calculate the PDF for the countable plate.
   • 0.2 ml/1 ml = 2/10 = 1/5
6. Calculate the FDF for the countable plate.
   • FDF = SDF x TSDF x PDF
   • FDF = 1/1 x 1/10 x 1/5 = 1/50
7. Calculate the CFU/ml for the countable plate.
   • CFU/ml = #CFU x 1/FDF
   • CFU/ml = 250 x 1 / 1/50
   • = 250 x 50
   • = 12,500 CFU/ml
   • = 1.25 x 10

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