Subtract till 100

Calculate:

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

55	-	25	=
68	-	30	=
3	-	2	=
59	-	46	=
30	-	27	=
79	-	42	=
88	-	42	=
8	-	7	=
78	-	43	=
88	-	20	=