1997*0.3/1999*0.5+1.2/1999 简便运算

1997*0.3/1999*0.5+1.2/1999
=1997*0.6/1999+1.2/1999
=(1997*0.6+1.2)/1999
=(1997*0.6+0.6*2)/1999
=(0.6*(1997+2))/1999
=(0.6*1999)/1999
=0.6