Subtract till 100

Calculate:

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

80	-	3	=
59	-	23	=
31	-	29	=
84	-	46	=
61	-	42	=
92	-	41	=
89	-	18	=
64	-	39	=
86	-	15	=
89	-	7	=