1. The problem statement, all variables and given/known data Find exactly the volume in the first octant under the planes x + z =1 and y + z =1. Find the mass if the density is p(x,y,z)=xyz. 3. The attempt at a solution This is a pyramid in shape, so for the volume, rather than constructing a double integral, I used the formula V= Bh/3 which is equal to 1/3. Please see the jpg file for the work on finding the mass. Where did I go wrong? It came out to be 0. I tried reversing the z limits and that didn't do anything.