A disinfectant spray bottle says it eliminates 90% of bacteria with each application. You apply the disinfectant once to a count

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A disinfectant spray bottle says it eliminates 90% of bacteria with each application. You apply the disinfectant once to a count

ertop in the shipping department and then apply the disinfectant again to the same countertop. If the bottle is correct, what percentage of the bacteria originally on the tabletop have been eliminated?

Advanced Placement (AP)

1 answer:

kotykmax [209] · Answer 1 · 2026-02-19T15:37:07+03:00

Applying the disinfectant once removes 90% of the bacteria, leaving 10% remaining.

Applying it a second time eliminates 90% of that remaining 10%, so you calculate 10 minus 90% of 10 to find the leftover bacteria after two applications.

$.90 * .10 = .09$

$.10 - .09 = .01$

This results in only 1% of the bacteria still being present, meaning that 99% of the original bacteria have been eradicated.