Mishnayos Maaser Sheni Perek 4 Mishnah 8

המניח איסר – to be redeemed upon the produce of Second Tithe, and it was already redeemed.

ואכל עליו חציו והלך למקום אחר – and he carried the Issar with him, and there it is worth a Pundiyon, and at first, he would not leave other than with one-half a Pundiyon, for the Pundiyon is equivalent to two Isaarim. It would be found that according to what he currently goes out with what remains is an Issar of non-sacred produce and therefore he consumes from it another Issar.

אוכל עליו עוד פלג – one-half Issar, and we don’t say that since it is not worth other than an Issar, that he actually ate all of it.

המניח איסר של מעשר שני – in order to eat of it as his non-sacred produce in the sanctity of [Second] Tithe. And he consumes from it until eleven per Issar, and one one-hundredth of an Issar, all of his Issar became non-sacred. But if the Issar was from the Second Tithe monies of that were certainly tithed, and he consumed from that total until there remained in it one out of one-hundred, such as one hundred figs are sold for an Issar, and he consumed ninety-nine of them, all of them became non-sacred produce.

וב"ש אומרים הכל עשרה – One of them was most certainly tithed and another was doubtfully tithed, if there did not remain from that Issar other than one-tenth, it became non-sacred produce., such as the case where there were ten pomegranates that were sold for an Issar, and he consumed nine of them that became non-sacred produce, if there remained additional produce, such as if he had only consumed eight [out of ten], he must consume the corresponding amount.

וב"ה אומרים: - בודאי אחד עשר ובדמאי עשרה – if there remained of the Issar of definitely tithed produce an Issar’s worth eleven, he is obligated to consume another [one part], since all whaich is less than the equivalent of a penny, we are not concerned for him, not for the matter of theft, nor the matter of benefiting from that which is dedicated to the Temple. A Perutah/penny is one-eighth of Italian Issar – hence, one tenth of an Issar is eight tenths of a Perutah which is equal to a Perutah less twenty percent. It turns out that when one adds twenty-percent which is one-quarter from the inside which is equal to one-fifth on he outside, there will be [amongst] everything a penny/Perutah. And therefore, we are concerned for this, for if there will be less than one-tenth, we don’t worry, for even with the addition of an additional fifth there will be in it less than the equivalent value of a Perutah. And therefore, they said, that with a definitively-tithed produce, eleven, and with doubtfully-tithed produce ten, since we are not obligated [an additional] one-fifth on that which is doubtfully-tithed, and the one-tenth is less than the equivalent of a Perutah. And the Halakha is according to the School of Hillel.