Suppose you have a 9 quart container and a 4 quart container. How can you
obtain exactly 6 quarts of water in the large container?

Let's abreviate "the 9 quart container" as " the 9QC" and 
the 4 quart container as "the 4QC" 

1.  Fill the 9QC from the faucet or river.

2.  Fill the 4QC from the 9QC, leaving 5 qts. in the 9QC.

3.  Empty the 4QC.

4.  Fill the 4QC from the 9QC, leaving 1 qt. in the 9QC.

5.  Empty the 4QC.

6.  Pour the 1 qt. from the 9QC into the 4QC, leaving room in
         the 4QC for 3 qts.

7.  Fill the 9QC from the faucet or river.

8.  Finish filling the 4QT from the 9QC, which will 
         amount to pouring off 3 qts. from the 9QC leaving 6 qts.
         in the 9QC.


Edwin
AnlytcPhil@aol.com