Question

a person goes from a sauna at 115°F to an out side temperature of -30°F. what is the change in temperature?

Answer 1

Whenever you're interested in computing the (absolute) difference between two values of a certain variable, you have to subtract the final value and the initial value. This is often written as delta:

$\Delta x = x_{\text{final}} - x_{\text{initial}}$

So, in this case, the final temperature is -30°F. The initial temperature is 115°F. So, the variation is

$\Delta T = T_{\text{final}} - T_{\text{initial}} = -30 - 115 = -145$

A negative delta indicates that the value decreased, which is our case.