In a well-insulated container of negligible heat capacity, $100\ \text{g}$ of ice at $-10^\circ\text{C}$ is mixed with $200\ \text{g}$ of water at $50^\circ\text{C}$. The specific heat of ice is $0.5\ \text{cal g}^{-1}\,{}^\circ\text{C}^{-1}$, the specific heat of water is $1\ \text{cal g}^{-1}\,{}^\circ\text{C}^{-1}$, and the latent heat of fusion of ice is $80\ \text{cal/g}$. The final temperature of the mixture, in degrees Celsius, is ____.