Subtract till 20

Calculate:

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

95	-	10	=
74	-	21	=
20	-	20	=
97	-	42	=
52	-	29	=
60	-	31	=
78	-	23	=
36	-	11	=
28	-	28	=
57	-	10	=