Gd5(SixGe1-x)4 for 0.41≤x≤0.5 is orthorhombic and ferromagnetic at lower temperature, monoclinic and paramagnetic at higher temperature, and shows a first order magnetic-structural phase transition between the two. Magnetic moment versus magnetic field (MH) isotherms were measured just above the first order transition temperature for Gd5Si1.95Ge2.05 and Gd5Si2Ge2 samples and the field-induced coupled phase transition from paramagnetic/monoclinic to ferromagnetic/orthorhombic phase was observed. Using the method developed by Arrott [Phys. Rev. 108, 1394 (1957)], the ferromagnetic portions of the MH isotherms were used to project the second order magnetic phase transition temperature of the orthorhombic phase, a region where the transition does not occur due to the first order transition at a lower temperature. These data points fall on the extrapolated line of the second order phase transition, drawn from the Si-rich region of the phase diagram.