For 1 x 10-6 dilution, the plating factor is . To find the number of bacteria in the original sample, the plating factor is multiplied by the colony count per ul.
<em>Number of viable bacteria = plating factor x colony count/ul</em>
Since 10 ul gives 64 colonies. 1 ul will give:
64/10 = 6.4 colonies.
Therefore, the viable bacteria in the original sample = 6.4 x cells/ul
It should be the last one, but if you can pick more than one answer then I would do the first and last one but I’m confident that it would be the last one either way :) hopefully this is helpful