I think , if we add some air - it will increase it's weight.
So, I think we must open the top of the water tank and we must show those water to sun and then the sun will absorb. those water!
HAHAHA . :lotpot3:
[quote="IMORTAL SOUL"]A tank of water weighs 50 pounds.What must you add to it to make it weigh 30 pounds?
[/quote]