Question

A disinfectant spray bottle eliminates 90%of bacteria each application. If you apply once on counter top then apply another on the same countertop. What percentage of bacteria has been eliminated?

Answer 1

I'd say still 90%

Explanation:

The other 10% of bacteria that was left over was probably immune or unaffected by the disinfectant, hence why the spray didn't kill 100% to begin with.

Its similar to hand sanitizer, It kills 99.99% of germs because one germ is always immune or unaffected by it. Hope that makes sense and helps!