The document discusses several problems that are hard to parallelize, including matrix-vector multiplication and matrix-matrix multiplication. It describes 1D and 2D assignment approaches to parallelizing matrix-vector multiplication across multiple processors. 1D assignment distributes the rows of the matrix and vector across processors, while 2D assignment distributes them in a 2D grid. It also outlines map-reduce approaches to parallelizing vector-matrix and matrix-matrix multiplication, breaking the problems into mapping and reducing stages.