Derangements
In the last section, we observed an instance of how $ e $ relates to probability, specifically the binomial distribution. Now, we will consider its relationship with derangements and will explain how, along a similar concept, it proves important in key ways. We will begin with an example to illustrate this property. Consider the following description of a Secret Santa gift exchange, which will be used to illustrate the properties relating $ e $ to derangements in this section.
- Around certain holidays, such as Christmas, one popular tradition among friends is to organize a gift exchange, in which each person buys a gift for another randomly selected participant, but recipients do not know from whom they are receiving their gift. To accomplish this, it is often standard to participate in a drawing, of sorts, in which everyone's name is put into a hat, and each person draws a name to determine for whom they will be getting a gift.
- Because everyone wants to be surprised by the gift they receive, however, this method only works when no one happens to draw their own name. If this does occur, the names must be redrawn, which can lead one to consider how often this method will work the first time. To accomplish this, let us observe all permutations pertaining to who draws which name and determine which cases will have every person draw someone else's name.
What are Derangements?
