\begin{definition}[Definition:Donkey and Mule Problem]
A '''Donkey and Mule problem''' is of the form:
:$2$ participants are comparing their quantity of goods they own relative to the other.
:Participant $1$ suggests transferring some of the goods of one of them to the other, and remarks on their relative quantities after that exchange.
:Participant $2$ then suggests the same (or a similar) thing, but transferring the goods in the other direction, and again remarks on their relative quantities after that exchange.
From these remarks, $2$ simultaneous linear equations can be set up and (assuming the question is well-crafted) solved.
The name comes from the original setting of this problem concerning a '''donkey''' and a '''mule''' each carrying a number of sacks.
\end{definition}