Ive been pondering this problem and don't know the answer.

Imagine a surface contaminated by germs. A cleaning product which claims to kill 99.9% of germs is used to wipe over the surface. According to the product's claim only 0.1% of the germs were resistant to the product and have survived, the other 99.9% have been killed. Now leave these resistant germs to repopulate the surface.

Now you have a surface populated by the germs that the cleaning product couldn't kill the frst time.

My question is if you use the cleaning product again will it be effective in killing 99.9% of these germs or will it simply do nothing?