A colony of bacteria originally contains 900 bacteria. It doubles in size every 30 minutes. How many hours will it take the colony to contain 9000 bacteria?

Answer 1

After 30 minutes, the colony will contain 900 x 2 = 1800 bacteria.
After 60 minutes (2 x 30 minutes), the colony will contain 1800 x 2 = 3600 bacteria.
After 90 minutes (3 x 30 minutes), the colony will contain 3600 x 2 = 7200 bacteria.
After 120 minutes (4 x 30 minutes), the colony will contain 7200 x 2 = 14400 bacteria.

Therefore, it will take 2 hours (120 minutes) for the colony to contain 9000 bacteria.

Answer 2

900(2^t) = 9000 , were t is the number of 1/2 hours
2^t = 10
t log2 = log 10
t =1/log2 = 3.322 half hours
t = 1.67 hours or 1 hours and 40 minutes