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GATE Civil Engineering (CE) 2021 Shift 1 Solved Paper

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Question : 43

Total: 65

A water sample is analyzed for coliform organisms by the multiple - the fermentation method. The results of the confirmed test are as follows:

Sample size (mL)	Number of positive results out of 5 tubes	Number of negative results out of 5 tubes
0.01	5	0
0.001	3	2
0.0001	1	4

The most probable number (MPN) of coliform organisms for the above results is to be obtained using the following MPN Index.

MPN Index for Various Combinations of Positive Results when Five Tubes used per Dilution of 10.0 mL, 1.0 mL, and 0.1 mL
Combination of positive tubes	MPN Index per 100 mL
0 – 2 – 4	11
1 – 3 – 5	19
4 – 2 – 0	22
5 – 3 – 1	110

The MPN of coliform organisms per 100 mL is

110000
1100000
110
1100

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