One dollar

Heard the story from M.

In a charity fair, there was a sale on books - 3 dollars for each.

There were plenty of people choosing the books as they were really in bargain sale - all the books were contributed by the people for charity purpose.

For the easy administrative work, the rule was - "no change", all the money went into the box. It would also welcomed people to pay more in kind or contribute their change as well.

A man chose three books and he paid 10 dollars into the box.

Then, he left.

Later on, the man came back and he chose again another two books.

But this time, he insisted to pay only 5 dollars, as he said that just now, he paid one dollar more, with that dollar, and the 5 dollars, it covered two books' cost.

The man spoke loudly and insisted to do so.