Adding till 20

Calculate:

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

2	+	4	=
5	+	9	=
5	+	3	=
3	+	1	=
2	+	1	=
11	+	6	=
10	+	6	=
9	+	8	=
5	+	4	=
2	+	2	=