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Randy Spencer
Joined: 03 Jun 2003 Posts: 8 Location: Vigo

Posted: Tue Mar 01, 2005 9:47 am Post subject: Positive & negative numbers in everyday use 


I have just completed Unit 7. We used the number line, slide rule, along with the calculator for figuring problems with negative numbers. I was also able to show them on the number line what was happening when we subtracted. I was taught the rules for subtracting a negative number & accepted them without question. I had someone ask me why is it a positve when you subtract a negative number. Can someone share some practical examples that might occur with a student when subtracting negative numbers to get a positive? 

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Julie Rosner Sigmund
Joined: 03 Jun 2003 Posts: 36 Location: Pike

Posted: Tue Mar 08, 2005 6:29 pm Post subject: negative numbers 


Randy,
This made me think. I am sharing one thing that came to mind. Hopefully I can explain it well online. When we are first teaching positive and negative numbers, one tool we use are the positive and negative counters. One thing that I tried to show subtracting a negative can give you a positive involves using the counters. I'll start with an easy example. Use 5 negative counters to show 5. Use these counters to first solve 55. The students would have the 5 negative counters. Then they would take away () 5 negative counters (5) and get the answer of zero.
This second problem will be a little more complicated. In order to show a problem such as 56, the students will need to start with a way to show 5 using BOTH positive and negative counters. For example, they could draw 8 negatives and 3 positive counters to give a balance of 5. Then they could actually take away 6 negative counters. They would be left with 2 negative counters and 3 positive counters  by cancelling out, they would be left with 1 positive counter. So, 56=+1.
This was hard to describe without drawing a picture. I hope it makes sense. If not, remind me and we can talk about it at our next meeting in Indy.
Good luck!
Julie 

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