The temperature decreased 3 degrees per hour from 9pm to 2am. write and evaluate an expression to represent the overall change in temperature

It may help to look at an actual thermometer. It will look something

like this:

|

+ 40

|

+ 30

|

+ 20

|

+ 10

| ^

+ 0 / \

| |

+ -10 | warmer (increasing temperature)

| |

+ -20 +

| |

+ -30 | colder (decreasing temperature)

| |

+ -40 \ /

| V

Suppose it was -20 degrees an hour ago, and now it has gone down 10

degrees. As it goes down, it will get farther away from 0 (since it

is below zero to start with), so it will decrease from -20 degrees

to -30 degrees! The number part (the 30, which is the "absolute

value" of the temperature) increases because we are going away from

zero while the temperature itself decreases (getting colder). If the

temperature changed to -10, it would be warmer, not colder; that would

be an increase in temperature.

Does that make sense?