21. A membrane filtration plate count method is used to analyse microbial contamination in a water sample. 1 mL of sample is serially diluted in six test-tubes as shown in the figure below and 10 mL is filtered through a membrane which is transferred onto media in a 12 cm diameter petri dish. The number of colonies observed in the three top plates is 98, 34 and 5 as shown in the Table 1. Using statistical considerations and the recommended ranges from the Standard Methods, (a) Determine the number of colony forming units (CFUs)/100 mL in the original sample based on the colony count from plating Test Tube 6 only. ( 5 pts ) (b) What will be the most correct reported colony count in the original sample if the practitioner applied good judgement on the observed data and consideration for allowable counts per plate according to Standard Methods for Membrane Filtration Method? ( 25 pts ) (c) Determine the representation error in the reported data if, in a rush, the practitioner only reported data obtained from the last test tube. [Null Hypothesis of one sample against a sample] ( 16 pts ) Table 1: Microbial contaminants Heterotrophic count method. Plate No. Colony Count Number in Original Plate Represented / 100 mL 4 98 ? 5 34 ? 6 5 ? 10 mL