Hopefully I can describe this problem correctly.
Let's say you have 2 objects, and you want to randomly choose between the two objects. You can do this by devising a function that can give a 50% chance to choose one of the objects.
Now, let's say you have chosen this object, and you now introduce a new object. You want to make a new choice, between this already-chosen object, and this newly introduced object. You want to devise a function such that overall, there was still an equal likelihood of choosing each of the three object. However, at this point, you only have the result of the first choice, and the newly-introduced third object.
I was told the answer was to give a 2/3 weighting to the already chosen object, and give a 1/3 weighting to the third object. However, my gut is telling me this is wrong, but I can't explain why. Is this actually correct?