An Ar/Ca abundance ratio of at least 0.56 is derived using the X-ray spectra of solar flares recorded by the SOLFLEX spectrometers on the P78-1 spacecraft. The method involves determining the contribution of the Ar XVII 1s2 1S0-1s4p 1P1 line to a blended feature at 3.2005 A. This contribution is determined by considering the relationship of the other component of the blended feature, namely the Ca XVIII 1s2 2s 2S(1/2)-1s2p2s 2P(3/2) line, to the dielectronic satellite lines of Ca XVII that fall between 3.215 and 3.24 A. It is demonstrated that a broad-wavelength coverage solar X-ray spectrometer experiment is necessary for precise abundance measurements.