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Subtraction across zeros

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 Mandice77 Joined: Aug 2008 Posts: 31 Junior Member
Mandice77

Joined: Aug 2008
Posts: 31
Junior Member
Subtraction across zeros
09-28-2008, 06:24 PM
 #1

I have been teaching subtraction with re-grouping and across zeros for the past couple of weeks and the kids just aren't getting it. Does anyone have any creative ways to re-teach this?

 Raid14 Joined: Jun 2006 Posts: 476 Senior Member
Raid14

Joined: Jun 2006
Posts: 476
Senior Member
In the same boat...
09-28-2008, 06:57 PM
 #2

My co-teacher and I have not had such a struggling group of math students before. Our first goal has been to work on subtraction with regrouping. It's been a month, but we are seeing some progress.
We went online and used the National Library of Virtual Manipulatives. In the 3-5 section, there is a place where you can do base blocks addition. We really had to explain what was happening and why because most kids thought it was just a "game" and weren't connecting it to the actual subtraction problem, but I think it helped a lot of the kids see what the regrouping actually looked like!

 jjwires Joined: Jun 2007 Posts: 4,371 Senior Member
jjwires

Joined: Jun 2007
Posts: 4,371
Senior Member

09-29-2008, 06:18 PM
 #3

Have you tried using play money? Use pennies, dimes, and dollars. Once they see that they don't have enough of one and they must borrow from either the dimes or dollars it usually clicks!

I've also had them box in the hundreds and tens number on the top if they have to borrow. Then they take one away from the number they boxed in. Hope this makes sense.

 Carolina Girl Joined: Sep 2007 Posts: 314 Full Member
Carolina Girl

Joined: Sep 2007
Posts: 314
Full Member
Subtraction across zeros
09-29-2008, 06:30 PM
 #4

Years ago when I began teaching, a veteran teacher taught me to do it this way: When you have a number like 700 - 364, have students underline the zero in the tens place and continue to underline until they come to a number other than zero. In the above example it would be the number 7. Students would see that they have underlined the number 70. Ask them if they would be able to borrow from 70. They see that it is possible. Guide them into crossing out the 70, making it 69, and then they are able to make the zero in the ones place the number 10. Once they do this, there is no regrouping to do. The 69 that was written makes it easy for students to complete simple subtraction.

This may seem vague initially, but once students see it, they love it because they don't have to keep marking out numbers. My last two classes have caught on quickly. Even this year, one of my students from 2 years ago came by to tell me that even her 5th grade teacher does it this way, and that she (the student) continues to do it this way.

Good luck!

 Roxi Joined: Jun 2007 Posts: 190 Full Member
Roxi

Joined: Jun 2007
Posts: 190
Full Member
PT taught me this last year...
09-29-2008, 07:56 PM
 #5

...and I LOVED it!! After I teach regrouping and make sure they understand the concept, I teach this trick.

Using whiteboards, I ask, "WHat is 1 less than 5000?"
We do several of these questions and then move to:

1000-224= 999-224+1.

Then there is no regrouping.

 LAthird Guest
LAthird

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Brilliant!
09-30-2008, 05:28 PM
 #6

Roxi, I love that idea. I just finished teaching this last week, but I'm going to show this to the kids tomorrow. Y'all are so much help here.

 ETG Guest
ETG

Guest
subtraction across zeros
10-16-2008, 08:55 AM
 #7

My best advice, and my colleagues agree, is to not try to get the students to regroup into a ten when there is a zero and then subtract from the ten to make nine. I tell my students that you regroup from "whoever" is next door. If "someone" is there, then you take 1. If "no one is there, then you keep moving down the street until you find someone home and you subtract from that entire number". So if you're subtracting 89 from 306, you cannot subtract 9 from 6 so you go nextdoor. But no one is there so you keep moving. Using the marker, you have marked through a 30 so you subtract 1 from 30 leaving a 29. Bring back the one you took making a 16. Then you can subtract. It's the same principle but leaving out the middle step and my kids always get it quickly.

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