Example of two IMFs (one shown in blue, one in orange) with different numbers of CCSNe. The number of CCSNe equals the integral from the least massive star to contribute to SF to the most massive star. The areas below the functions, therefore, show the number of CCSNe that are expected to explode before SF ends for the case that all stars up to a mass of 150 M_⊙ explode in a CCSN (squares) and the case that only stars below 20 M_⊙ explode (stars). In this work the mass of the least massive star to explode (lower boundary of the coloured areas) is computed from the known number of CCSNe and the known mass of the most massive star to explode.