Need help with a math problem

[Armageddon415]

Heres the problem:
You have two containers, one of which contains 9 liters of liquid when filled and the other contains 4 liters when filled. How can you measure out exactly 6 liters of liquid in the 9 liter container without using any other tools?

I remember something like this in one of the Die Hard movies where they had to measure a certain amount of water to keep a bomb from exploding.

 

[gopunk]

fill the 4 and dump into 9
fill the 4 and dump into 9. 9 now has 8

fill four and dump as much as you can into 9. 9 now has 9 and 4 now has 3.

empty the 9

now transfer the 3 in 4 to the 9. so now 4 is empty and 9 has 3.

fill up 4, and dump into 9, so now 9 has 7.
fill up 4 again and dump as much as you can into the 9. now 9 has 9 and 4 has 2.

now dump the 9, transfer 4 to 9, fill up 4 again, and dump into 9 to get 6

 

[Armageddon415]

Thanx

 

[Lars]

fill 9 dump into 4 (9 has 5, 4 has 4)
empty 4 and dump 9 into 4 again (9 has 1, 4 has 4)
empty 4 and dump 9 into 4 (9 has 0, 4 has 1)
fill 9 and dump into 4 (9 has 6, 4 has 4)