Subtract till 100

Calculate:

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

59	-	42	=
26	-	23	=
61	-	48	=
40	-	28	=
78	-	44	=
6	-	4	=
71	-	26	=
78	-	18	=
89	-	10	=
10	-	10	=