A certain culture of bacteria quadruples every hour. If a container with these bacteria was half full at 10:00 a.m., at what time was it one-eighth full?

Question: A certain culture of bacteria quadruples every hour. If a container with these bacteria was half full at 10:00 a.m., at what time was it one-eighth full?

Solution:
To go from one-eighth (1/8) full to half (1/2) full culture of bacteria should quadruple: (1/2) ÷ (1/8) = (1/2) × 8 = 4
As it quadruples every hour then container was one-eighth full at 10:00 a.m - 1 hour = 9:00 a.m.