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We prepared a polycrystalline sample of orthorhombic La0.7Ca0.2Sr0.1MnO3 and then investigated its magnetic properties. Detailed studies and analyses in the vicinity of the ferromagnetic (FM)-paramagnetic phase-transition temperature prove the sample undergoing a second-order phase transition, where variations of the saturation magnetization and the initial susceptibility versus temperature obey asymptotic relations. Basing on the modified Arrott plot, we have determined the critical parameters (TC, β, γ, and δ) in the two characteristic regions of low- and high-magnetic fields, and in the cases of no-subtracting and subtracting the demagnetization field (Hd). The experimental results reveal that values of the critical parameters depend remarkably on analysis routes of isothermal-magnetization data. Intrinsically, β keeps close to the value expected for the 3D Heisenberg ferromagnets with ferromagnetic short-range interactions, while γ is close to the value of the mean-field theory. These results are different from those reported previously on a La0.7Ca0.2Sr0.1MnO3 single crystal exhibiting a tri-critical point. The effects related to grain boundaries and isotropic properties existing in the polycrystalline sample are assigned to cause such the phenomena. Particularly, around TC, the magnetic-entropy change reaches a maximum value of 4.3 J kg-1 K-1 under an applied field of 30 kOe, which corresponds to a relative cooling power ∼150 J/kg suitable for magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]