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adding
subtract
adding
subtract
100

2+2

2+2=4

100

2-1

2-1=1

100

15+10

15+10=25

100

100-50

100-50=50

200

15+15

15+15=30

200

2-2

2-2=0

200

50+50

50+50=100

200

200-100

200-100=100

300

100+100

100+100=200

300

25-10

25-10=15

300

20+30

20+30=50

300

300-100

300-100=200

400

30+30

30+30=60

400

50-30

50-30=20

400

25+25

25+25=50

400

500-100

500-100=400

500

125+125

125+125=250

500

100-100

100-100=0

500

15+100

15+100=115

500

1,000-900

1,000-900=100