\begin{definition}[Definition:Cistern Problem]
A '''cistern problem''' is one which concerns the rate of flow of a liquid into or out of a cistern.
The givens are usually the rates, or relative rates, of flow of each of a number of pipes flowing into or out of the cistern, or possibly both.
What is required is usually the length of time it takes to fill or empty the cistern when all the pipes operate together.
Hence the more general application, where the problem consists of:
:a specific task
:a number of resources whose job it is to fulfil that task
:the length of time it takes those resources, or specific combinations of those resources, to accomplish that task
:the total length of time it takes all of those resources together to fulfil the task.
A popular instance of this problem is that of a number of farm hands, all of whom work at different rates, whose task it is to reap a field.
\end{definition}