Temperatures The most extreme temperature change in Canadian history occurred when the temperature in Pincher Creek, Alberta, rose from $-19{}^{\circ }\text{C to 22}{}^{\circ }\text{C}$in one hour. Find the change in temperature.

Two numbers with similar signs get added and the resulting number carries the similar sign.

Two numbers with opposite signs get subtracted and the resulting number carries the sign of the larger number.

The temperature at the start of the hour is $-{19}^{o}C$. The temperature at the end of the hour is ${22}^{o}C$.

The change in a quantity is found by subtracting the initial value of the quantity from the value after change.

So, the difference in temperature is given by the difference of final temperature minus the initial temperature. That is,

$22-\left(-19\right)$

To evaluate the difference $22-\left(-19\right)$, we will add the opposite of the second number with the first number. That is, add the opposite of –19 with 22.

To subtract $-19$, add its opposite 19 with the first number to get

Thus, the difference of the numbers is ${41}^{o}C$.