I've found the following statement on the web:
"The only temperature represented as a prime number in both Celsius and Fahrenheit is X°C (=Y°F).
a. Is there really only one couple (X,Y) fitting the above description?
b. Does it apply to positive values only?
To quote Wikipedia: A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself.
Other definitions are in line with this. Which seems to answer part b.
The F to C formula C=(5/9)(F-32) guarantees integers only if C is a multiple of 5 and F is 32 more than a multiple of 9 (5 mod 9)
Thus for a couple to exist C must be 5 and indeed F is 41 which is also prime.
The only solution to part a. is (5,41)
If you instead asked for |X| and |Y| to be prime you could also get a solution of (-5,23). I assume this is what part b. is hinting at.
Posted by Jer
on 2017-11-03 10:14:18