 Uncontroversial facts about probability reveal the mistake and establish the correct answer. For the next test to be on Wednesday, there would have to be a conjunction of two events: no test on Tuesday (a 5/6 chance of that) and a test on Wednesday (a 1/6 chance). The probability for each subsequent day becomes less and less. (It would be astounding if the next quiz day were a hundred days from now!) The question is not whether a six will be rolled on any given day, but when the next six will be rolled. Which day is the next one depends partly on what happens meanwhile, as well as depending partly on the roll of the die on that day.