(1)609+306-708-108+202-198+497-100
=600+300-700-100+200-200+500-100+9+6-8-8+2+2-3
=500;
(2)999+998+997+996
=1000+1000+1000+1000-(1+2+3+4)
=4000-10
=3990.
(1)609+306-708-108+202-198+497-100
=600+300-700-100+200-200+500-100+9+6-8-8+2+2-3
=500;
(2)999+998+997+996
=1000+1000+1000+1000-(1+2+3+4)
=4000-10
=3990.