The number of bacteria in a petri dish increased by 20 percent every 2 hours. If there were 72 million bacteria in the dish at 6: 00 p.m., at what time were there 50 million bacteria in the dish? Choose the most appropriate option:
A) 6: 00 p.m.
B) 8: 00 p.m.
C) 2: 00 p.m.
D) 8: 00 a.m.
E) 12: 00 p.m.
Given:   he number of bacteria in a petri dish increased by 20 percent every 2 hours   There were 72 million bacteria in the dish at 6: 00 p.m   Since the bacteria is increasing by 20% every 2 hours, this means that the number is multiplied by 1.2 every 2 hours.   Required: At what time were there 50 million bacteria in the dish?   Assume that there were n intervals of 2 hours between 50 million and 72 million.   50 * (1.2)^n = 72   (12/10)^n = 72/50 = 144/100 = (12/10)^2   Hence n = 2 intervals.   Each interval was of 2 hours. Therefore, the number of hours = 4   Subtracting 4 hours from 6 PM, we get 2 PM as the answer.   Option 2: 00 p.m.
<result>C</result>
The number of bacteria in a petri dish increased by 20 percent every 2 hours. If there were 72 million bacteria in the dish at 6: 00 p.m., at what time were there 50 million bacteria in the dish?