Return Calculation Private Wealth always, numbers, correct, question, positive

cfalevel2011

Really dumb question, but is there a rule that anyone has to keep what numbers are negative and positive in the FV, PV, PMT calculations when doing an IRR type of calculation? Looking at the 2008 exam, part D, the if the the PMT is positive if the PV is negative in order to get the correct answer... I always thought you start with the PV as negative, and then the PMT or cash flow would be negative if an outflow, or positive if an inflow.... anyone?