Adding till 20

Calculate:

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

13	+	6	=
10	+	8	=
4	+	9	=
5	+	11	=
8	+	6	=
5	+	3	=
6	+	6	=
8	+	8	=
15	+	3	=
9	+	10	=