How can this lab illustrate this fact

Question

person is slightly denser than water. Life preservers are made of low density materials.  The average density of a person plus a life preserver is less than density of water- so together they will float. Therefore when objects more dense than water are joined to objects less dense than water, the entire unit will float if the overall density of combination is less than that of water

Answer 1

What is your question?  Apparently you did a lab involving density, but it isn't clear what you did or what question you have.  Density is defined as mass per unit volume, or mass/volume. It is generally expressed as grams/ml (g/ml, or gcm³), but can have other units of mass/volume.