Show:
Add to 20
Subtract within 20
Add to 50
Add to 100
Repeated Addition
100

4+4

8

100

10-2

8

100

25+11

36

100

23+54

77

100

2+2+2

6
200

2+8

10

200

5-3

2

200

16+23

39

200

38+51

89

200

4+4+4

12
300

7+6

13

300

17-7

10

300

39+7

46

300

71+26

97

300

5+5+5+5

20

400

8+7

15

400

20-7

13

400

22+24

46

400

35+43

78

400

1+1+1+1+1+1+1

7

500

12+5

17

500

18-6

12

500

33+17

50

500

81+12

93
500

6+6+6+6

24