[QUOTE=Dr Sardonicus;480037]SOP for multiple-choice questions is that there is only one correct answer. So if two of the alternatives are identical, both are wrong.

In a 4-choice question, this would leave two possible answers. Selecting one of these two possibilities at random would mean a 50% chance of choosing the correct answer.

Curiously, 50% is one of the answers on offer.[/QUOTE]But, by eliminating 2 of them, it is no longer at random. Once you delete choices, the randomness goes away.

[QUOTE=Uncwilly;480039]But, by eliminating 2 of them, it is no longer at random. Once you delete choices, the randomness goes away.[/QUOTE]

I voted wrong but I can get to 66% in a similar way the two left behind are 2 of three distinct answers. Mathematically random is such that all possibilities are equally likely so the distinct value consideration is valid.