I'm sorry but it's pretty impossible to answer this in such generic terms. It really depends on the situation that you encounter.
However, generally speaking Monitor & Control Project Work is generally performed to ensure that we are following the project management plan. Control Costs is performed to monitor the project status in regards to cost and Control Schedule for the schedule. And yes... I know... that's not very specific and informative.
But like I said it all depends on the scenario that is presented to you. The best suggestion I have for you is to continue answering exam sample questions and get more exposure to questions about these processes and basically learn from your correct/incorrect answers.
Until Next Time,
Cornelius Fichtner, PMP, CSM
President, OSP International LLC
Moderators: Yolanda Mabutas, Ahmed Amin, Scott Gillard, Mary Kathrine Padua, ERIC BARTLETT, Gail Freedman, Kevin Nason, Steven Mudrinich, PMP, Mark Wuenscher, PMP, John Wolverton, Tracy Shagnea, PMP, Jada Garrett
This interview with Simona Fallavollita (LinkedIn Profile) was recorded at the magnificient Project Management Institute (PMI)® Global Conference 2017 in Chicago, Illinois. We discuss the how, what, why and when of the changes that are coming to the PMP exam.