Based on a practice exam from practicequiz.com the ROM show the estimate to be -50% to 50%. It was noted this question was recalled on the PMI exam. There may be some confusion with aspirants who need the knowledge base to understand what is definitively correct. I would recommend a in-dept online tutorial or seek professional education guidance on this question.
PMBOK page 201
For example, a project in the initiation phase may have a rough
order of magnitude (ROM) estimate in the range of −25% to +75%. Later in the project, as more information is
known, definitive estimates could narrow the range of accuracy to -5% to +10%. In some organizations, there are
guidelines for when such refinements can be made and the degree of confidence or accuracy that is expected.
Can u help me, as in when these estimates are done(process group) as I am coming across question for the same !
Rough Order of Magnitude estimate = -50% to +50% - INITIATION
Preliminary estimate = -15% to + 50%
Budget estimate = -10% to +25%
Definitive estimate = -5% to +10%
Final estimate = 0%
Sana, You are correct that memorizing the types of estimate ranges is easier than some other complicated formulas. I am not sure about the question you are talking about, but I think any question about estimate types will give you a clue about the answer. Perhaps the words in the question might say Top Down or Bottom Up. Perhaps it might say they project manager has to get an estimate very quickly. Other clues might indicate where you are in the project management process. If you are in initiating phase, then a rough order of magnitude would be the correct choice.
As for additional training, if you are on this discussion, then you might know that PM Prepcast has an exam simulator for purchase. Another source of PMP training that really, in my opinion, makes learning easy is the Head First series.
Training for Project Management Professional (PMP)®, PMI Agile Certified Practitioner (PMI-ACP)®, and Certified Associate in Project Management (CAPM)®