In commemoration of 19 Kislev - the anniversary of the release of the Baal HaTanya, the founder of Chabad, from prison in Russia 215 years ago - a sale of chassidic sefarim took place in Yerushalayim. Sefarim and discs of chassidic music were sold at a flat rate of four for NIS100, but you had to buy in blocs of four.

Menachem was interested in purchasing two discs. “Do you know anyone going to the sefarim sale?” he asked his friend Mendel.

“I’m going,” replied Mendel. “Do you want me to buy something?”

“I’d like two discs,” said Menachem. He gave Mendel NIS50, and Mendel agreed to get two extra books and add another NIS50 to make up Menachem’s bloc.

At the sale, Mendel chose ten sefarim: eight for his own NIS200, and two more to complete Menachem’s bloc, totaling NIS 250. He then got the discs for Menachem and was pleased to see that the two discs counted only as one sefer.

“Great!” Mendel said. “I can get an additional free sefer for myself.” He added an eleventh sefer to his cart.

When Mendel returned, he gave the discs to Menachem. “Thank you,” said Menachem. “What sefarim did you buy?”

“I bought a new nine-volume edition of Sfas Emes,” replied Mendel, “and two other sefarim.”

“Eleven sefarim?” asked Menachem, puzzled.

“Your two discs counted as a single sefer,” replied Mendel, “so I was able to get another one for myself.”

“What do you mean, for yourself?” said Menachem. “You owe me NIS25 change!”

“But we agreed that you would pay 50 for the two discs,” said Mendel. “If it was less, that’s my gain!”

“Why?” argued Menachem. “I made a mistake. I didn’t know the discs cost only 25.”

“I only agreed to add 50,” countered Mendel. “I don’t know that I would have spent another 75. Anyway, you couldn’t have gotten the discs for 25. They sold only in blocks of 100. If not for my other 50, your discs alone would still cost 100!”

“By the same logic, your two sefarim would also have cost 100,” retorted Menachem. “They required my discs.”

“I wonder what Rabbi Dayan has to say about this.” said Mendel. “Let’s ask him!”

“You should split the cost of the third sefer,” answered Rabbi Dayan when they approached him.

“Why shouldn’t I be entitled to the full NIS25 change?” asked Menachem.

“Had it been possible to purchase the discs alone for NIS25, Mendel would have to return the full 25 to you,” explained Rabbi Dayan. “He was simply your agent to purchase the discs, at whatever price they cost. However, Mendel correctly pointed out that the discs alone could not be purchased for 25 without his sefarim. At the same time, the two sefarim that Mendel wanted to buy could also not be purchased for 50 without your discs. Between your money for the discs and his money for two sefarim, you were entitled to a fourth sefer.”

“So why split it?” asked Mendel.

“There are two reasons,” replied Rabbi Dayan. “First, in the case of two people who were partners in an endeavor, and the capital of both was necessary to earn profit, the Gemara (Kesubos 93a-b) rules to split the profit equally. Some explain that this applies even if the partners did not have equal shares in the capital, especially if the profit is a single item not fit to divide (C.M. 176:5; Pischei Teshuvah 176:3; Pischei Choshen, Shutfim 3:17).

“Second, in the case of someone who bought something on behalf of his friend and the storeowner added a bonus, the Gemara (Kesubos 98b) rules that the customer whose money it is and the agent who came to the store should split the bonus (C.M. 183:6).

“Thus, since the extra sefer was due to the purchase of both the discs and the other two sefarim, and since Mendel was the agent to buy the discs, you should split the extra sefer. Mendel should return 12.5 NIS.

“Alternatively,” concluded Rabbi Dayan, “since Menachem was willing to spend 50 anyway, Mendel could have bought him a sefer with the extra money.”