The table of increase looks something like this:

Time (minutes) 0 40 80 120 160 etc

# Bacteria 10 20 40 80 160

So, you will have a factor of 2 each time. If B = # Bacteria & t = time

Let **B = (10)*2**^{(t/40)}** ** then each time the time increases by 40 minutes, you double the number.

Check at each point to be sure it is accurate!