Hint



Click the box that contains the correct rule for each sum.
Add 0
Add 1
Add 2
57 +
= 57
68 +
= 70
93 +
= 94
69 +
= 70
78 +
= 80
99 +
= 99
46 +
= 48
1 +
= 1
19 +
= 20