Here is what the Kollel wrote about this subject in our Insights to the

Daf for Chulin 95a.

Best regards,

Mordecai Kornfeld

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2) "ROV" AND "KAVU'A"

QUESTION: The Gemara teaches that when one bought a piece of meat from a store but does not know whether he bought the meat from a Kosher meat store or from a non-Kosher meat store, and there are nine Kosher stores and one non-Kosher store, the meat is prohibited. However, when he found a piece of meat outside of a store, the meat is permitted because we follow the majority (Rov). The principle of Rov resolves a doubt only with objects that "separate themselves" from a group. When the object is "Kavu'a" (established in its place), the Safek remains and each possibility is considered to be equally plausible.

What is the logic behind this ruling? The statistical probability in each case -- a case of Rov, when the objected became separated from the group, and a case of Kavu'a, when the object is still in its place -- is exactly the same in both cases.

ANSWER: HAGA'ON RAV YISRAEL ZEV GUSTMAN zt'l explained that the answer to this question depends on how the Safek is expressed. In a case of an object that separated from a group that contained objects of Isur and Heter, the Safek is expressed as the question, "From which of the objects in the group did this one separate?" If most of the objects in the group are Heter, then the object that separated from the group is permitted as well.

In contrast, when an object is found in its place, the Safek is expressed as the question, "Some of the objects here are Mutar and some are Asur. Is this particular object Mutar or is it Asur?" Since the question has only two sides (Mutar and Asur), it is considered to be an equally balanced Safek. (M. Kornfeld)