解:61.9+16.8-1.9+13.2=(61.9-1.9)+(16.8+13.2)=60+30=90
61.9+16.8-1.9+13.2=61.9-1.9+16.8+13.2=60+30=90
61.9+16.8-1.9+13.2=90
61.9+16.8-1.9+13.2=61.9-1.9+(16.8+13.2)=60+30=90
61.9+16.8-1.9+13.2=61.9-1.9+(16.8+13.2)=60+30=90