Adding till 20

Calculate:

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

13	+	6	=
7	+	9	=
1	+	3	=
7	+	7	=
5	+	4	=
7	+	12	=
2	+	1	=
11	+	5	=
11	+	9	=
5	+	8	=