1)350-166=184
2)238+175=413
3)497,498,499,500,501,502,503,504,505,506,507,508-a
757,756,755,754,753,752,751,750,749,748-b
990,991,992,993,994,995,996,997,998,999-c
4)a)999
b)102
c)101
5)a)300,300,500,500,700
b)860,880,590,760,640
6)446+379=825-a)
513-275=238-b
(608-459)+249=149+249=547-c