What is the answer to the riddle The Liar and the Truth-Teller?

Answer 1

This is a clear case of using a double negative on the lier while using a positive on the truth teller. The only distinction between any question is though the use of the brothers directly. So something like this would work:

"which door would your brother say leads to misery".

The truth teller would tell what his brother would tell, which is a lie. So he would point to not the misery by the prosperity.

The lier would lie and say the opposite of what his brother would say. The truth teller would point to misery so he would lie and point to prosperity.

Both Brothers will point your way to prosperity.