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Equal masses of three liquids x, y and z are at temperatures 10 deg C, 20 deg C and 30 deg C respectively. Mixing x with y gives an equilibrium temperature of 16 deg C, and mixing y with z gives 26 deg C. What will be the equilibrium temperature when x and z are mixed?

1. 28.32 deg C
2. 25.62 deg C
3. 23.84 deg C
4. 20.28 deg C

Correct answer: 23.84 deg C

Solution

The two given mixings fix c_y/cₓ and c_z/c_y; using these in the x-z heat balance gives T = 77.5/3.25 = 23.85 deg C, i.e. about 23.84 deg C.

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