E. coli is among the fastest-growing bacteria, with a generation (or doubling) time of 20 minutes under optimal conditions. After 60 minutes, the number of bacteria in a culture of E. coli was 400 . Approximately how many bacteria were in the culture after 30 minutes? Choose 1 answer: (A) 50 (B) 142 (c) 174 (D) 200

Question

E. coli is among the fastest-growing bacteria, with a generation (or doubling) time of 20 minutes under optimal conditions. After 60 minutes, the number of bacteria in a culture of E. coli was 400 . Approximately how many bacteria were in the culture after 30 minutes? Choose 1 answer: (A) 50 (B) 142 (c)  174 (D)  200

Bytelearn · Accepted Answer

Understand the problem: Understand the problem. We know that E. coli bacteria double every 20 minutes. After 60 minutes, the culture has 400 bacteria. We need to find out how many bacteria were present after 30 minutes, which is one generation or doubling time before the count reached 400.Determine doublings in 60 minutes: Determine the number of doublings that occurred in 60 minutes. Since the doubling time is 20 minutes, and we are looking at a 60-minute period, we can calculate the number of doublings by dividing 60 by 20. 60 minutes ÷ 20 minutes per doubling = 3 doublingsFind bacteria count after 30 minutes: Work backwards to find the number of bacteria after 30 minutes. Since the bacteria count is 400 after 60 minutes (3 doublings), we need to divide by 2 to find the count after 2 doublings (which is 30 minutes less). 400 bacteria ÷ 2 = 200 bacteria

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