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When 100 g of a liquid A at 100°C is added to 50 g of a liquid B at temperature 75°C, the temperature of the mixture becomes 90°C. The temperature of the mixture, if 100 g of liquid A at 100°C is added to 50 g of liquid B at 50°C, will be:

1. 60°C
2. 70°C
3. 85°C
4. 80°C

Correct answer: 80°C

Solution

From case 1: 100 c_A (100-90) = 50 c_B (90-75) gives c_A/c_B = 0.75. Case 2: 100 c_A (100-T) = 50 c_B (T-50) -> 75(100-T)=50(T-50) -> 125T=10000 -> T = 80 C.

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