Ask any of the guards “what would the other guard say if I ask him the way of hell?”
If you end up asking the question to the truthful one, he knows that the other guard would lie so, he will tell the truth and the way to exit.
If you end up asking the question to the liar guard, he knows that the other guard would have truthfully shown you the way to hell, but as he is a liar, he will lie about it and show you the way to exit.
Take four random men and set them aside. Now, weigh the remaining eight men on the seesaw, four on each side. One of the two things will happen.
1. The seesaw will balance perfectly. It means, that the light man is amongst the four men you set aside earlier. Use your second turn to weigh those four (two on each side) to see which side is heavier. At last, use your third and final seesaw turn to weigh those last two men to find the light man.
2. The seesaw will not balance perfectly. Now when you know that one of the four men on one side is light. Follow the steps just like scenario 1. above. Use your second turn to measure the four men, two on each side, then use your third and final seesaw turn to find out which of the man is lightweight.