Angel I beleive you are right!!!
I'm going to answer #3. Try to ignore the part in the midle if you others want to answer without seeing mine.
#3 Fill the 3 liter, dump all into the 5 liter, fill 3 liter again, fill 5 liter, which will leave 1 liter in the 3 liter conatiner, empty 5 liter, put the 1 liter in the 5 liter container, and add one more full 3 liter container, giving you 4 liters in the 5 liter container.