解:51×0.51━0.5=51×(0.5+0.01)-0.5=51×0.5+51×0.01-1×0.5=(51-1)×0.5+51×0.01=50×0.5+0.51=25+0.51=25.51
51×0.51━0.5=(50+1)*0.51-0.5=25.5+0.51-0.5=25.51
51×0.51-0.551×0.51-0.51+0.01=(51-1)×0.51+0.01=50×0.51+0.01=25.5+0.01=25.51