0.9+9.9+99.9+999.9
=1-0.1+10-0.1+100.0.1+1000-0.1
=(1000+100+10+1)-(0.1+0.1+0.1+0.1)
=1111-0.4
=1110.6
0.9+9.9+99.9+999.9=1+10+100+1000-0.1×4=1111-0.4=1110.6
0.9+9.9+99.9+999.9=1+10+100+1000-0.1-0.1-0.1-0.1=1111-0.4=1110.6