Комментарий к Махширин 2:11

פירות שניה שרבו על של שלישית – The first year and second [year] of the Sabbatical cycle one [has the] practice [of giving] First Tithe and Second Tithe on them, and similarly in the fourth and fifth [years]. But in the third and sixth [years], [one gives] First Tithe and the Poor Man’s Tithe.

Introduction During the first, second, fourth and fifth years of the sabbatical cycle second tithe is taken out from produce. This tithe must be consumed in Jerusalem, or at least exchanged for money and separated in Jerusalem. In the third and sixth years the poor tithe is taken out and given to the poor. Seventh year produce is holy and it is forbidden to conduct business with it (i.e. sell it for a profit). Our mishnah deals with produce from the second year which are mixed with third year produce or other such mixtures. Makhshirin If the produce of the second year exceeded in quantity the produce of the third year, or the produce of the third year exceeded the produce of the fourth year, or the produce of the fourth year exceeded the produce of the fifth year, or the produce of the fifth year exceeded the produce of the sixth year, or the produce of the sixth year exceeded the produce of the seventh year, or the produce of the seventh year exceeded the produce of the year after the conclusion of the seventh year, we follow the majority. If half and half, the rule is stringent.

ושל שביעית – which has In it the sanctity of the Seventh Year and one is exempt from the tithe. And in regard the matter of all of these laws, it is taught that one follows after the majority.

The rule here is quite simple we follow the majority of the produce. Note that some of these possibilities are not really important, since the produce of those two years has the same status. For instance, if fourth and fifth year produce are mixed up, it doesn't matter because one takes second tithe from both. The mishnah just runs through the whole list of possibilities.

מחצה למחצה להחמיר – But in regard to a doubt of Second Tithe and the Poor Man’s Tithe, he should separate out one tithe, and profane the produce over the money, and separate the divide up the produce among the poor and consume the monies [of Second Tithe] in Jerusalem. But in regard to doubt regarding Seventh Year produce, they are liable for tithes and liable for the Holiness of the Seventh Year [produce] to not use them for business or for puffed up cheeks, and they are liable for removal of tithes (see Deuteronomy 26:13).

If the mixture is evenly split, we follow the strictest possibility. So if we are not sure if second tithe or poor tithe should be taken out he would have to take out both, and bring the second tithe to Jerusalem (or redeem it for money) and give the poor tithe to the poor. If there is a possibility that the produce is sabbatical year produce, then it all must be treated with the appropriate sanctity and one could not engage in business with it.