Menahot, Chapter Thirteen, Mishnah Two
1) [If he said] A minhah or a kind of minhah, he may bring one [of any kind].
2) [If he said] Menahot or A kind from menahot, he must bring two [of any one kind].
3) [If he said,] I specified [a certain kind], but I do not know what kind I specified, he must bring the five kinds.
4) [If he said,] I specified a minhah of [a certain number of] tenths but I do not know what number I specified, he must bring sixty tenths.
a) But Rabbi says, he must bring menahot [of every number] of tenths from one to sixty.
Section one: Again, this is a general introduction to the rest of the mishnah. If he pledges to bring a minhah or kind of from the various types of menahot he must bring one minhah.
Section two: If he uses the plural, he must bring two, because the minimum of a plurality is two.
Section three: There are five different kinds of menahot mentioned in Leviticus 2:
1) A minhah of choice flour.
2 + 3) A minhah baked in the oven. There are two kinds of such minhahs: loaves, and wafers.
4) A minhah cooked on a griddle.
5) A minhah cooked in a pan.
If he remembers that he specified that he wished to bring a certain type of minhah, but he doesnt remember what type he specified, he must bring one of each type, lest that is the type that he pledged.
Section six: Here he remembers what type of minhah he specified, but he does not remember how many tenths he pledged to put in the minhah. As we have seen, a minhah can have anywhere from 1-60 tenths of flour.
According to the first opinion, he must bring one minhah of sixty tenths, because that is the maximum amount of tenths that a minhah can consist of. Rabbi works the math out differently. The problem with bringing one minhah of sixty tenths is that the one who made the pledge might have said a minhah with a lower amount, in which case the minhah with sixty tenths would not fulfill his pledge. What he must do is bring a minhah for every number from one to sixty. This way he can be covered for every possibility. I wont do that math here, but suffice it to say that this forgotten pledge is going to cost him a bundle!