Where do we subtract negative numbers IRL?

[PeterPan]

I was wanting some physical examples of subtracting negative numbers, and I was sort of drawing a blank. I ended up using an example I found online of a soup pot with magic hot (+) and magic cold (-) cubes. I've seen cats and dogs, but it doesn't really EXPLAIN it, only demonstrates. It's subtracting the negatives she'd like to see happening in real life. It's sort of an oddball thing when you think about it, lol.

[Osmosis Mom]

I guess if you owe money and then get some and need to repay?? Or you owe money and then you owe some more?:lol:

[Capt_Uhura]

Yep, I usually think in terms of money when discussing negative numbers. If a store lets you run a tab until you get paid, and you take $10 worth of merchandise, you now have -$10. If the next week, you take $20 worth of merchandise, you now have -$10+(-20)=-$30. But if you work a day for the store owner, you don't have to repay the $20 so you have -$10-(-$20)= -$10+20=$-10. Is that what you're asking?

[dm379]

My bank account has negative numbers all the time. :tongue_smilie:

[Jamee]

Tempratures? My DH uses a model of above sea level and below sea level when introducing negative numbers with the numbers under water, the negative ones.

[KarenNC]

Tempratures? My DH uses a model of above sea level and below sea level when introducing negative numbers with the numbers under water, the negative ones.

 

 

This is the model we used. You could also use the timeline for BCE/CE, I suppose, but that's a bit more abstract.

[Capt_Uhura]

Was coming back to post that I also use temperature.

[onaclairadeluna]

I teach that the negative can also mean a direction change. I teach subtracting negative numbers using a number line.

[Spy Car]

Football.

 

Like when the Quarterback gets sacked for a loss of 8 yards on first-down, and it's now second-down and 18.

 

Bill

[stripe]

My kids were kicking around the problem -100 - (-100) yesterday and they were leaning towards saying it was 200. I asked them, "What's the difference between -100 and -100?" and they said, "Zero."

 

So that's subtraction as a difference.

 

You can do something similar with temps or sea level, as described.

 

Here are some other ideas.

http://mathforum.org/library/drmath/view/57870.html

including the idea of using it as a direction, similar to SpyCar's sports example

http://mathforum.org/library/drmath/view/57869.html

[Nakia]

My bank account has negative numbers all the time. :tongue_smilie:

 

That's what I was thinking! :lol:

[wy_kid_wrangler04]

My bank account has negative numbers all the time. :tongue_smilie:

 

That's what I was thinking! :lol:

 

 

 

:lol:

[EKS]

It was 80 degrees this morning and -20 degrees this afternoon. What was the change in the temperature over the course of the day? 80 - (-20) = 100 degrees

[woolybear]

When I pay my bills! :eek:

[PeterPan]

Thanks ladies! I'll have her read through these with me. We got sidetracked for a couple days with some Home Ec. (Read: we had to clean like crazy for someone coming over. ;) )