You want to know how long it'll take for the bacteria to grow
to (800/500) = 1.6 times their initial population.
The number of double-times it'll take is
[ log(1.6) / (log(2) ] = 0.6781 .
The double-time for these particular critters is 12 hours,
so it'll take them
0.6781 x 12 hours = 8.137 hours
= 8 hours 8.2 minutes .
