A bacteria culture starts with 500 bacteria and doubles in size every half hour.1
(a) How many bacteria are there after 3 hours?
We are told “. . . doubles in size every half hour.” Let’s make a table of the time and population:
t 0 0.5 1.0 1.5 2.0 2.5 3.0
bacteria 500 1000 2000 4000 8000 16000 32000
Thus, after three hours, the population of bacteria is 32,000.
(b) How many bacteria are there after t hours?
In t hours, there are 2t doubling periods. (For example, after 4 hours, the population has doubled 8
times.) The initial value is 500, so the population P at time t is given by
P(t) = 500 · 2
2t
