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At what temperature does the reading on a Centigrade thermometer equal the reading on a Fahrenheit thermometer placed in the same liquid?

1. -40 deg C
2. 0 deg C
3. 100 deg C
4. 300 deg C

Correct answer: -40 deg C

Solution

Solving C = (9/5)C + 32 gives C = -40, where both scales coincide.

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