QUESTION:
If I put a tank of water on the scales and it weighs 30 lbs. and I put a
live 10 lb. fish in it. What will be the total weight of the tank and fish
on the scale. How will buoyancy play in this, and what would happen if
the fish died and sank to the bottom or floated to the top? 
  

ANSWER Bonnie P. Dalton on January 9, 1998: 
I believe while you are in an atmosphere with gravity, that is you are 
weighing the tank and fish here on earth, you will always have a total of 
40 lbs whether the fish is in the tank or laying beside the tank while both 
are on the scale. Where the fish goes should be irrelevant while your 
weighing is being done under gravity conditions. 
  

ANSWER from Duncan Atchison on January 9, 1998: 

Total weight of the tank and fish would be 40 lbs, regardless of whether 
the fish remains alive or dies.