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?

Virtually every anti-bacterial cleaning product that I buy claims to that it will kill 99.9% of bugs. So my questions is - what type of bacteria or viruses are the 0.1% that these products can't kill? They really must be the sort of thing that you wouldn't want to meet down a dark alley.

We recently had a new kitchen installed at home, included was a glass topped halogen hob. Soon after - and much to her disappointment - my mother split some sugar on the hot hob while making jam. As the manual said, the hob was allowed to cool off before cleaning; however when it came to cleaning off the hardened sugar globules they took some glass away with them, leaving a sprinkling of pits in the surface.

No abrasives were used in cleaning, just hob cleaner and a sponge, what happened?