Adding till 20

Calculate:

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

3	+	5	=
10	+	4	=
9	+	11	=
7	+	11	=
7	+	8	=
4	+	9	=
5	+	8	=
3	+	3	=
5	+	11	=
2	+	3	=