Good day and thanks for your message. Please accept my apologies for the late response. I usually get an email notification when there is a post at the forum. Although your post was successful at the forum, somehow I missed the email notification.
Let’s break your problem into two parts:
1. What is a ROM ?
2. How would you calculate ROM in your Exam
Regarding ROM, as I have explained before, there is no hard and fast rule for calculating the ROM. The PMBOK4 said it’s plus/minus 50%. But now the PMBOK 5 pre-release edition says it’s from -25% to +75%. In theory every estimate that has a wide estimate range is a rough order estimate. For your example, if the target price is $100,000 then both $50,000 to $150,000 and $75,000 to $175,000 are rough order estimates; both are correct answers.
Now, let’s address your exam concern. For the exam questions, I would strongly recommend going for the PMBOK ranges. The PMBOK4 will be tested till June 2013, till then plus minus 50% is your guideline. If you see a -50% to +50% choice, choose that as your correct answer. If -50% and +50% is not available as one of the choices, search for the -25% and +75% choice. If both are not available, then pick the widest range. Remember, for the real exam, you need to make the best choice.
Another tip, use sample exam questions on internet as a tool to help you prepare for the exam. These are indeed very close to the PMI exams but are not from the PMI. The PMI PMP exams are filtered by many experts before they appear in an exam. You won’t see a question on the real PMP exam that asks you to identify the ROM and has both -50% to +50% and -25% to +75% as two choices to pick from.
Please let me know if that clears your confusion. If I have still failed to clear your confusion, please let me know if it is the ROM concept that is troubling you or some specific sample exam question?