200 g of water at 80 °C is mixed with 300 g of water at 20 °C. Assuming no heat loss, what is the final temperature?
Correct answer A. 44 °C
Explanation
Heat lost = heat gained: 200(80 − θ) = 300(θ − 20), giving 500θ = 22000 and θ = 44 °C. A simple average of 50 °C ignores the unequal masses.
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