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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

E. coli is among the fastest-growing bacteria, with a generation (or doubling) time of 2020 minutes under optimal conditions. After 6060 minutes, the number of bacteria in a culture of E. coli was 400400. Approximately how many bacteria were in the culture after 3030 minutes?\newlineChoose 11 answer:\newline(A) 5050\newline(B) 142142\newline(C) 174174\newline(D) 200200

Full solution

Q. E. coli is among the fastest-growing bacteria, with a generation (or doubling) time of 2020 minutes under optimal conditions. After 6060 minutes, the number of bacteria in a culture of E. coli was 400400. Approximately how many bacteria were in the culture after 3030 minutes?\newlineChoose 11 answer:\newline(A) 5050\newline(B) 142142\newline(C) 174174\newline(D) 200200
  1. Understand the problem: Understand the problem.\newlineWe know that extit{E. coli} bacteria double every 2020 minutes. After 6060 minutes, the number of bacteria is 400400. We need to find out how many bacteria were there after 3030 minutes, which is one generation or doubling time before the count was 400400.
  2. Determine doublings in 6060 minutes: Determine the number of doublings that occurred in 6060 minutes.\newlineSince the doubling time is 2020 minutes, in 6060 minutes there would be 60/20=360 / 20 = 3 doublings.
  3. Calculate bacteria after one fewer doubling: Calculate the number of bacteria after one fewer doubling.\newlineTo find the number of bacteria after 3030 minutes (which is one doubling time before 6060 minutes), we divide the number of bacteria at 6060 minutes by 22 (because the population halves as we go back one doubling time).\newline400/2=200400 / 2 = 200

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