Adding till 20

Calculate:

Number of examples:
Numerical difficulty:
Range of values:
Multiplicity:

9	+	6	=
8	+	3	=
8	+	10	=
8	+	12	=
6	+	9	=
4	+	4	=
2	+	3	=
9	+	10	=
3	+	4	=
3	+	3	=