What are two ways that the term "the devil's arithmetic" is used in the book?
I would say that the concept of the "devil's arithmetic" is used in two specific ways in Yolen's work. One way in which the concept is used is to explain how survival is possible in the camp. For those who lived in the camp, there was an awful and incomprehensible formula which determine who would live and who would die. In a struggle to find meaning, "the devil's arithmetic" is a means to help explain issues of life and death in the camp. From a philosophical standpoint, it was a way to bring order into an existence that lacked it and defied logic and reasoning. Similar to this, the "logic" of the method was used to determine a code of conduct on how to live in the camp. We can see that "the devil's arithmetic" served two functions. The first was to explain how death was decided and the second was how one should live. Within this discussion is the larger issue of how structure and order was determined by the devil and not God. In this light, those who were in the camp, struggling to find meaning, recognized that God was absent and in its place, there had to be some order, which became "the devil's arithmetic." In this configuration, there is both a statement on faith and consciousness, with both overlapping one another.
One way is that the name is practically saying "This is the performance of the Devil" or something like "The Devil caused this." or "Only the Devil would perform something like this."
Another way is that even though things may be awful, you can live through it because the Devil is not impossible.
Did this help you? I hope so!