3.
Takes chicken across
Comes back alone
Takes dog across
Brings chicken back
Takes corn across
Comes back alone
Takes chicken across

8.
1st use of scale - put 3 coins on each side.
If they are level,
2nd use of scale - compare the 2 coins not weighed in the first use, the heavier 1 is counterfeit.
If they are not level,
2nd use of scale - take coins from the 3 that were heavier in the 1st weighing, and compare them. If they are equal, the other one is counterfeit. If not, the heavier one is.