Adding till 20

Calculate:

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

4	+	4	=
7	+	11	=
3	+	6	=
1	+	2	=
5	+	6	=
2	+	3	=
5	+	3	=
2	+	1	=
7	+	7	=
9	+	7	=