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
Q. 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
Understand the problem: Understand the problem.We know that extit{E. coli} bacteria double every 20 minutes. After 60 minutes, the number of bacteria is 400. We need to find out how many bacteria were there after 30 minutes, which is one generation or doubling time before the count was 400.
Determine doublings in 60 minutes: Determine the number of doublings that occurred in 60 minutes.Since the doubling time is 20 minutes, in 60 minutes there would be 60/20=3 doublings.
Calculate bacteria after one fewer doubling: Calculate the number of bacteria after one fewer doubling.To find the number of bacteria after 30 minutes (which is one doubling time before 60 minutes), we divide the number of bacteria at 60 minutes by 2 (because the population halves as we go back one doubling time).400/2=200
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