+   +   12   +   +

 

NEGATIVE NUMBERS

 

The first time I formally introduced negative numbers as part of a counting lesson was when a fifth grader went into negative numbers while counting down in fours.  

And she did fine except for saying two minus, six minus, ten minus…  All I had to do was point out that convention requires us to say minus two, not two minus.

Introduce negative numbers early enough and kids soon learn that they are real – that what they represent really does exist.  It is after all a lot colder when the temperature is -20o than when it is -5o.

Do exercises like those set out here and both understanding the idea of negative numbers and how to work with them develop quite naturally.

It will also ready students to take higher-grade work in their stride.

1. It is winter and the outside temperature is -10°C. During the next hour the temperature falls two degrees.  What is the temperature now?

2. Later in the day it warms up 8°.  What is the temperature now?  

3. The temperature is 0°C.  A cold wind comes up and the temperature drops 4°.  How cold is it now?

4. Later still the wind dies down and the temperature climbs 5°.  What is your thermometer reading now?

5. The sun comes out and pushes the temperature up another 3°.  How warm is it now?

6. At sunset the wind comes up and pushes the temperature down 12°.  What is the temperature?

Adding and subtracting  temperature changes across  zeroo  is a good way of helping students come to understand why –

 

a plus and a plus makes a plus;

a minus and a minus makes a plus;

a plus and a minus makes a minus, and

a minus and a plus makes a minus.  

Variations on a theme:

 

1. On the way to school or home, add up number plate digits; e.g.,

                                 

                                           3 + 4 + 5 = 12

 

2. Find the difference between a number plate’s first two digits and the last one.

                            

                                           (1 + 3) – 6 = -2

 

Such exercises are important because they get students to take their math out on the street with them.

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