As a group, learners investigate three packages which are all the same size and shape, but have different contents. One is filled with foam, one is filled with wood, and one is filled with metal. Learners are introduced to the concept of density, that objects with the same volume but different masses have different densities. Learners can extend their learning using one of the extensions provided: twenty questions to determine contents, determine the volume of the packages, determine mass and densities of the packages. Part of the 21-activity guide published by OMSI, No Hassle Messy Science with a Wow. All activities in this guide use household materials and all lesson plans include preparation directions, demonstrations, procedure sheets, cross-curricular connections, and scientific explanation of content.