You can find this problem in https://www.gregmat.com/study-plans/week-1-of-the-two-month-study-plan → Day3 → Quant Practice: All Previous Concepts.

According to Greg, the answer is A-30. But isn’t 30 just the number of POSITIVE odd factors? What about the NEGATIVE odd factors? If we take negative odd factors into consideration, the answer should be 60 i.e. B.

Please help.