Subtract till 20

Calculate:

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

47	-	2	=
62	-	48	=
50	-	21	=
89	-	2	=
37	-	26	=
60	-	43	=
84	-	46	=
11	-	2	=
55	-	31	=
100	-	35	=