Adding till 20

Calculate:

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

5	+	7	=
2	+	1	=
3	+	2	=
5	+	5	=
3	+	1	=
5	+	2	=
3	+	3	=
9	+	10	=
4	+	4	=
4	+	5	=