Let’s assume various cutlery are mixed together so that they are a ta’aroves. Let’s say one needs ten forks for use for the upcoming meal. In regards to Borer, does one need to make sure that he selects exactly ten forks? Or, can one retrieve a bunch of forks without careful consideration of how many he is selecting (in which case he may end up selecting more than ten forks, which means that the extra forks would have been selected but not used for the upcoming meal)?
You can take as many forks as you reasonably need for the meal, without having to be concerned that you have to use each and every fork. However, you may not just take extras that you can assess that will not be needed at all. Even in retrospect, that you took an extra fork, and you didn’t end up needing it, it is not considered as if you did borer, because it was taken because you very possibly would need it for the meal.
M:B 319-5, Eyal Mesulash (Borer) 8-11.