I am having trouble with some math in my microbiology class. Here's an example of a problem:
Plating 1.0 mL of a sample diluted by a factor of 10 (to the -3 power) produced 43 colonies. What was the original concentration in the sample?

Question

I am having trouble with some math in my microbiology class. Here's an example of a problem:
Plating 1.0 mL of a sample diluted by a factor of 10 (to the -3 power) produced 43 colonies. What was the original concentration in the sample?

tkhunny · Answer

Not quite sure...let's see if we can make some sense of it.

What we know is that our sample is 1000 times larger (Dilution Factor $10^{-3}$) than it was before.

"43 colonies" doesn't change.  (theoretically)

43 colonies / 1.0 mL

1000 * (43 colonies / 1.0 mL) = 43 colonies / 1.0 $\mu$L