You prepared a tuna sandwich st 2pm, accidentally adding 100 salmonallae to it.

Question

You prepared a tuna sandwich st 2pm, accidentally adding 100 salmonallae to it. You know that 30,000 microbes are necessary to start infection and the replication rate of this particular salmonella is 20 minutes. When will your sandwich be unsafe to eat? You prepared a tuna sandwich st 2pm, accidentally adding 100 salmonallae to it. You know that 30,000 microbes are necessary to start infection and the replication rate of this particular salmonella is 20 minutes. When will your sandwich be unsafe to eat?

Explanation / Answer

To answer this question we have to split it into two parts:

1. We must calculate how many salmonellae are going to be grown in one hour. Since the replication rate of this bacteria is 20 minutes, in one hour it can replicate 3 times (60/20 = 3). So, in an hour we can expect the growth of 800 microbes. 100 microbes replicate to produces 200 microbes (1st cycle) 200 microbes replicates to produce 400 replicates (second cycle) and 400 microbes replicate to produce 800 microbes (third cycle).

2. Now by simple calculation, we can find the solution to this problem

1 hour = 800 microbes (in one hour 800 microbes are produced)

? hour (X) = 30,000 microbes (in how many hours 30,000 microbes will be produced)

by cross multiplication, we get X = 30000/800 = 37.5 hours.

The sandwich will be unsafe to eat after 37.5 hours. That is on the third day 3.30 AM.

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