Chapter 1 - Some Basic Concepts of Arithmetic and Algebra - 1.3 - Integers: Addition and Subtraction - Problem Set 1.3 - Page 20: 122

The temperature at 11 PM is $-11˚F$

Recall the following rule: $-a+(-b)=-a-b$ Thus, we obtain: $= (-6) + (-5)$ $= (-6) - 5$ $= -11˚F$ Initially, you have a temperature of $-6˚F$, which then drops by $5˚F$. The term "drop" suggests a decrease in temperature; therefore, you add $-5˚F$ to $-6˚F$ to find the temperature at 11 PM.