It has been 20+ years since I have done statistical calculations...so please bear with me for the simpleness of this.

For my son's 6th grade science class, I need to calculate the sample size.

The experiement is:

Swab household surfaces (toilets, doorknobs etc) and then wipe with bleach and re-swab. Plate on agar and grow bactetia. The hypothesis is that the bleach treated surfaces with kill 99.9% of bacteria (manufactors claims.)

I would like the confidence interval to be 95% and powered to 80%.

This is really simple, but I have spent a enough time online seaching a left my stats books at the office.

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