There is no math required for this one at all. All it takes is a little memory of elementary school science, which may be worse.
Let me know your answer in the comments.
Imagine that you are in possession of two pails of water. These pails are identical in every significant respect, save that one has a large chunk of wood floating freely inside it, while the other does not. Apart from that disparity, the two are filled precisely to the brim with freshly distilled water.
Which of the pails would be heavier?