microbiology question from the kaplan notes - eurogirl

[ArchivalUser]

Please someone explain to me, the exercise from the microbiolody book , 2004 edition at page 16, there is a typical question......maybe is very easy....I don't know why my mind is not making it up...please take a loo on it and let me know...thak you.....Also I type here the question:
Aflask is inoculated to a density of 3x10 to power 3 cells /min. What is the density of cells in the culture after 50 minutes if the generation time is 20 minutes and the lag time is 10 minutes?
Thank you!

[ArchivalUser]

50-10[lag time]=40min,ie 2 generation time.
so 3(x10 to power 3 cells /min.) x2=6 (after 1 gene ... time)
6( x10 to power 3 cells /min.) x2=12 (after 2 gene ... time)