We have 16 tanks in a 4x4 grid.

+--+--+--+--+
|1 |2 |3 |4 |
+--+--+--+--+
|5 |6 |7 |8 |
+--+--+--+--+
|9 |10|11|12|
+--+--+--+--+
|13|14|15|16|
+--+--+--+--+

All the tanks are empty, except the first one, which is filled. We'd like to drain it. If you drain the water outside of the tank system, certain baby animals will be very sad, but draining the water from one tank to another is alright.

There is a door between each pair of adjacent tanks (but no diagonal connections). If you open the door between two tanks, the water levels will instantaneously equalize. What's the most you can drain out of the first tank?

One can easily get it down to 1/72 of a tank, as follows:

Posted by Steve Herman on 2013-10-14 17:56:43