How much mass is typically ejected from a supernova? How much mass is released from a supernova of a 15 solar-mass star? 20? 25? What is the relation between star mass and mass ejected?
 A: I like to explain this using a figure from a talk by Marco Limongi some years ago.

Based on a given set of models, the $x$-axis shows the initial mass of the models and the $y$-axis the final mass. The different coloured layers show the composition of the star at the moment of collapse. The mass ejected in the supernova is the difference between the curve marked remnant mass, which specifies (for these models) how much matter became part of the remnant, and the final mass, which was the mass of the star at collapse, after it had already lost a lot during its life.
The interesting point in this prediction is the change between the supernovae that leave neutron stars versus those that leave black holes. At the boundary, there's a large drop in the supernova-ejecta mass, because the black hole doesn't have a surface off of which inward falling material can bounce.
But, though the broad trends are probably right, note that this is the result for a particular set of model assumptions (e.g. mass loss on the main sequence, supernova energy and dynamics). The amount of ejecta for the supernova of a given progenitor is an open question, and still subject to intense research.
