You could only have drawn a ball from box 1 or 2. Since box 3 does not have a gold ball, you can dismiss it entirely from the equation.
The only question now is if you drew a ball from box 1 or 2.
So, its a 50/50 chance.
Not that hard.
please be joking
you have 5 words to explain how i'm wrong, otherwise you're trolling.
5 words aren't enough because you have a fundamental misunderstanding of stochastics
if you draw a ball from the gold+silver box, the chance of getting the gold ball is only 50%
if you draw a ball from the 2gold box, the chance of getting a gold ball is 100%
the boxes themselves have equal probability when we don't know the result of drawing, but since we know a gold ball was drawn, we have more information and know it was more likely the 2gold box
tl;dr: see the post tc made above this one
you pick a box, then a ball. not the other way around. ---