The number of bacteria in a petri dish increased by 50 percent every 2 hours. If there were 108 million bacteria in the dish at 5: 00 p.m., at what time were there 32 million bacteria in the dish?
Answers
A) 11: 00 a.m.	B) 8: 00 p.m.	C) 6: 00 a.m.	D) 8: 00 a.m.	E) 10: 00 a.m.
Given:   The number of bacteria in a petri dish increased by 50 percent every 2 hours   There were 108 million bacteria in the dish at 2: 00 p.m   Since the bacteria is increasing by 50% every 2 hours, this means that the number is multiplied by 1.5 every 2 hours.   Required: At what time were there 32 million bacteria in the dish?   Assume that there were n intervals of 2 hours between 32 million and 108 million.   32 * (1.5)^n = 108   (3/2)^n = 108/32 = 27/8 = (3/2)^3   Hence n = 3 intervals.   Each interval was of 2 hours. Therefore, the number of hours = 6   Subtracting 6 hours from 5 PM, we get 11 AM as the answer.   Option 11: 00 a.m.
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The number of bacteria in a petri dish increased by 50 percent every 2 hours. If there were 108 million bacteria in the dish at 5: 00 p.m., at what time were there 32 million bacteria in the dish?