1) "Is the belt in the left hand box?"

2) "Is the belt in the left hand box?"

if you get two answers the same you know they are both false answers

- Two "No"s means the belt is in the left box so you can open it.
- Two "Yes"s means it isn't in the left hand box but you have a true and a false answer left so your next question should be :

- 3) "if my fourth question was whether the belt is in the right hand box what would you answer?" - he either tells the truth about his final answer (which is a lie) or a lie about his final answer (which is the truth) so this will always be a lie - so a "yes" means you can open the middle box and a "no" means you can open the right hand box

- 3) "if my fourth question was whether the belt is in the right hand box what would you answer?" - he either tells the truth about his final answer (which is a lie) or a lie about his final answer (which is the truth) so this will always be a lie - so a "yes" means you can open the middle box and a "no" means you can open the right hand box

- Is the belt in the right hand box? - if he says No as he must be lying then open the right hand box, otherwise :

- is the belt in the middle box? - if he says No as he must be lying then open the middle box, otherwise open the left hand one.

- is the belt in the middle box? - if he says No as he must be lying then open the middle box, otherwise open the left hand one.