Subtract till 20

Calculate:

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

10	-	5	=
18	-	8	=
7	-	6	=
7	-	5	=
6	-	3	=
10	-	9	=
9	-	9	=
15	-	6	=
9	-	2	=
9	-	5	=