>>13663438The following reasoning appears to give a probability of 1/2
Originally, all three boxes were equally likely to be chosen.
The chosen box cannot be box SS.
So it must be box GG or GS.
By hypothesis, the chosen box cannot be box GG.
So it must be box GS.
And by hypothesis, the chosen box cannot be box GS.
So it must be box GG.
So you choose a box and check all boxes that can possibly lead to that box being chosen.
And when you see a box chosen that doesn’t lead to the box you want, you choose another box and check that box.
So when you get to the box you want, you will not have made a mistake.
