# Temperature

Question:

What is the temperature when it’s twice as cold as zero degrees?

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C

A

P

T

A

I

N

I

N

T

E

R

V

I

E

W

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Solution: In order for this puzzle to make sense, the candidate must recalibrate the question. It’s good to have some knowledge of the common temperature scales and how to convert among them. Often a conversation between the candidate and the interviewer is required. One candidate offered this exchange:

CANDIDATE: Before I answer that question, I need to understand the scale. Zero degrees in what scale?

The interviewer may specify a scale or say, “We’re not sure.”

CANDIDATE: Since “cold” is really just absence of heat, let’s calculate how much heat we have to start with and then calculate half of that. We can calculate this problem in the familiar temperature scales of Fahrenheit and Celsius. The problem wouldn’t make sense in the Kelvin scale, where 0 degrees Kelvin is also known as absolute zero at which point all heat is gone. So I’m assuming we are talking about a starting temperature above absolute zero. Nevertheless, it’s convenient to work in the Kelvin scale. Absolute zero is about 273 degrees Celsius, or about 460 degrees Fahrenheit. So, starting in the Celsius scale, 0 degrees Celsius is 273 Kelvin. Half of that is 136.5 degrees Kelvin, or 136.5 degrees Celsius. In Fahrenheit, 0 degrees F is equivalent to 255.4 K. Twice as cold as 255.4 K is 127.7 K, or 230 degrees F.

Answer: 136.5 degrees K;  136.5 degrees C;   230 degrees F.

Extra credit: Mention that the absolute zero version of the Fahrenheit scale is the Rankine scale. Add 460 degrees to Fahrenheit temperatures to obtain the Rankine temperature. So 0 degrees Fahrenheit is 460 degrees Rankine, twice as cold of which becomes 230 degrees Rankine.