If you are ever tested on LCMs on the GMAT, the quantities involved will *always* be positive integers. You don't need to know what the LCM even means if one number is a fraction, let alone how to find it.
Nov 2011: After years of development, I am now making my advanced Quant books and high-level problem sets available for sale. Contact me at ianstewartgmat at gmail.com for details.
Private GMAT Tutor based in Toronto