20% is right.. but guess its messed up.. any short or clear.. way?
For Rate x Hours = constant means Rate and Hours are inversely proportional.
Hence if rate is multiplied by 5/4 (25% increase) hours must be multiplied by the reciprocal or 4/5 (a 20% decrease) to maintain inverse proportionality.
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993