I don’t remember ever seeing the conversion formula written with “9/5”.
When measuring volume, length and mass, the metric system has rendered fractions archaic. Because I’m US centric, I see the F/C conversion formula as a prod to join the modern world. The same world that has deprecated fractions. That’s where I saw a “little” irony in the author using them.
In other words, “9/5” isn’t ‘sciencey’ enough. :)
