Subtract till 100

Calculate:

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

70	-	48	=
73	-	43	=
55	-	19	=
77	-	25	=
81	-	24	=
60	-	28	=
57	-	24	=
78	-	2	=
70	-	22	=
23	-	23	=