Many projects mix elements of multiple methodologies
If requirements are well-understood, might use Waterfall model to define requirements & system design, then implement using Incremental Delivery performed in Scrum-like sprints
If requirements are vague, might use Iterative Refinement to clarify requirements, followed by Modified Waterfall to build final version (prototype is discarded)
Might Integrate & Configure a COTS platform for prototype
Might develop user interface with iterative refinement, but adopt another process for data store