3 characters (numerical digits, letters, images, etc) are chosen from a set of 10, without replacement.
There are 120 such codes, with each character appearing 36 times. ie. ABC, ABD, ABE, ... , GHI, GIJ, HIJ
How can these codes be put into four groups, so that each character appears 9 times in each group?
This can easily be break into 12 subgroups. (each letter appear 3 times in each group)
SubGroup1: ABC, BCD, CDE, DEF, ....
SubGroup2: ABD, BCE, CDF, DEG, ....
SubSubGroup3: ABE, ......
SubGroup4: ABF, ......
SubGroup5: ABG, .......
SubGroup6: ABH, .......
SubGroup7: ABI, .......
SubGroup8: ACE, BDF, ......
SubGroup9: ACF, BDG, ......
SubGroup10: ACG, .......
SubGroup11: ACH, ....
SubGroup12: ADG, ...
any combination of 4 subgroups in each group will give you a grouping you wanted