a/ $997+86=997+3+83=1000+83=1083$
b/ $37.38+62.37=37(38+62)=37.100=3700$
c/ $43.11=43.10+43=430+43=473$
$67.101=67.100+67=6700+67=6767$
$423.1001=423.1000+423=423000+423=423423$
d/ $67.99=67.100-67=6700-67=6633$
$998.34=1000.34-2.34=34000-68=33932$