201.1×1999-2012 ×199.8=2011×199.9-2012 ×199.8=(2012-1)×199.9-2012 ×199.8=2012×199.9-199.9-2012 ×199.8=2012×(199.9-199.8)-199.9=2012×0.1-199.9=201.2-199.9=1.3