Notice the case where 2 are correct. In this case, the solution is either ABD, ADC, or DBC, and I can pick either one with a 1/3 chance of it being correct. However, if I don't pick the correct one, I will always get a result of '1 correct' (if DBC is the correct answer, ABD has '1 correct' with the B and ADC has '1 correct' with the C; the same applies to the other choices if either ABD or ADC is the right answer). So, in this case, I can pick at random among the three until I get the correct answer.
|2 correct, possible answers: (3/23 entries)||ABD ||ADC ||DBC|
|1 correct, possible answers: (9/23 entries) ||ACB ||ACD ||ADB ||BAC ||BDC ||CBA ||CBD ||DAC ||DBA |
|0 correct, possible answers: (11/23 entries) ||BAD ||BCA ||BCD ||BDA ||CAB ||CAD ||CDA ||CDB ||DAB ||DCA ||DCB|