The growth rate of Escherichia coli, a common bacterium found in the human intestine, is proportional to its size. Under ideal laboratory conditions, when this bacterium is grown in a nutrient broth medium, the number of cells in a culture doubles approximately every 30 min.
(b) How long would it take for a colony of 50 cells to increase to a population of 1 million? (Round your answer to the nearest whole number.)