You are sampling a well for the concentration of bacteria growing within it. You are on site in the field, so you decide

[answerhappygod]

You are sampling a well for the concentration of bacteria growing within it. You are on site in the field, so you decide to take 900 mL and another 1200 mL to take back to your
Microbiology Lab. When you return your laboratory assistant prepares what you expected to be a standard dilution series, however, since they failed to read their lab
procedure this is what they actually did:
First, your lab assistant took 153 mL from the 900 mL solution you brought from the well anddiluted it with 3,256 mL of water; then 13 mL of this is added to 382 mL of water; next 12.4 mL of this is added to 6.23 L of water; finally 100 uL is added to 0.2 mL. You place 160 uL of the final dilution onto a nutrient agar plate and after 48 hours you have 144 colonies. What was
the original bacterial cell concentration in the well? In order to be considered safe the well
must have fewer than 3.0 x 105 cells/mL. Is the well safe?