Difference between Celsius and Fahrenheit leads to unexpected observations.

Question

Say city A has a temperature of 54 F(12.2 C) and city B has a temperature of 44 F(6.7 C). Their difference is 10 F which is about -12.2 C. I mean what!? This means that 44 F(6.7 C) > 54 F(12.2 C) or 12.2 C - 6.7 C = -12.2C. How is this possible? Is this question silly??

Answer 1

If two scales have non-coincident zeros, the quantity differences will have transformation law that is different from quantity itself:

$$ y =ax+b,\qquad \text{but}\qquad \Delta y = y_2-y_1 = (ax_2+b)-(ax_1+b)=a(x_2-x_1)=a\Delta x $$

For Fahrenheit and Celsius: $$ F = 1.8C+32,\qquad \text{but}\qquad\Delta F = 1.8\Delta C $$

so difference in 10°F is 5.55°C.

Answer 2

You're evaluating a difference of temperatures, not a temperature; since there are $9$ degrees Fahrenheit to $5$ degrees Celsius, the difference in temperature of the two towns, in degrees Celsius, is $$ \frac{5}{9}\cdot 10\approx 5.56 $$

The temperatures yesterday here were: maximum $5$℃, minimum $-3$℃. They correspond to $41$℉/$26.6$℉.

The difference in degrees Celsius is $8$, which corresponds to $$ \frac{9}{5}\cdot 8=14.4 $$ degrees Fahrenheit, and this agrees with the given data. The fact that a temperature of $14.4$℉ is about $-9.78$℃ is of no concern.