Subtract till 20

Calculate:

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

14	-	5	=
7	-	6	=
18	-	3	=
19	-	5	=
20	-	6	=
20	-	8	=
8	-	6	=
5	-	5	=
11	-	3	=
11	-	5	=