Maaser Sheni, Chapter Two, Mishnah Five
This mishnah deals with maaser sheni coins (money that had been used to redeem maaser sheni produce) and hullin, non-sacred coins, that were mixed up together. The mishnah assumes that the person knows how many of the coins were maaser sheni, but he doesnt know which coins are maaser sheni.
1) Hullin coins and second tithe coins which were scattered together: whatever is picked up [one at a time] belongs to second tithe until the sum is completed, and the remainder is hullin.
2) If they were so mixed up as to be taken up by the handful, [they are divided] according to the proportion.
3) This is the general rule: what is picked up [one at a time] must be first given to second tithe, but [what is picked up] mixed [quantity is divided] according to the proportion.
Section one: If the coins are scattered such that he picks them up one at a time, then the first coins he picks up are maaser sheni, until he has picked up the number of coins that he knows were originally maaser sheni. The remaining coins are hullin. It doesnt really matter which coins were originally whatall that matters is that in the end, there are just as many maaser sheni coins as there were in the beginning. According to the Yerushalmi, he also needs to say, If that which I picked up first was not maaser sheni, then let the [real] maaser sheni be redeemed for these coins.
Section two: But if he gathers them all together and picks up a handful of them, then they are divvied up according to the proportion. So if originally half the coins were maaser sheni and half hullin, then half of the coins in his hand are maaser sheni and half are hullin.
Section three: This is the general rule that sums up the examples in the beginning of the mishnah.