Adding till 20

Calculate:

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

5	+	2	=
1	+	3	=
4	+	4	=
5	+	4	=
4	+	3	=
6	+	12	=
5	+	3	=
8	+	5	=
8	+	10	=
1	+	9	=