rant about handwash soap

all right now i feel like i want to make some little calculation after seeing a handwash soap advertisement. they say that washing your hands with that soap eradicates 99.99% of the bacterium that exist there, so let's calculate a bit.
warning: latex from an online latex equation editor dead ahead!

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From this source, I obtained that average E. coli bacteria is long and wide. That means its average area is . Meanwhile from another source, the average length of an adult male's hand is , and the average breadth is , which means that the average area is


It is multiplied by 2, because... average people have 2 hands. Yeah, common sense.

Now, the average hand can be fully occupied by bacterium.

Everytime you wash your hand, there's always of the bacterium left, and as the amount of bacterium existing is always a non-negative integer (no way you can have a one and a quarter of a bacterium, and it's still living), we can set up an inequality.










where is the ratio, that is, and is the number you have to repeat washing your hands to ensure no bacteria exists anymore.

Conclusion

Since must be a non-negative integer also, to ensure the amount of bacterium existing on your hand is less than 1, (which means 0 as it is a non-negative integer) you must wash your hand with that handwash soap at least 3 times to ensure total eradication of the average E. coli bacteria.

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Source (opens in new window) :
1. ^ Bacterial cell structure - Wikipedia
2. ^ Hand - Wikipedia