Adding till 20

Calculate:

The number of examples:
Numerical difficulty:
Range of values:
Multiplicity:

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