I teach them "add the opposite." Leave the first number alone, then handle the problem this way: For this problem, -7 - (-5) =

I make them make 2 marks on their paper (for any subtraction problem.) And we do it as we say Add (first mark) the Opposite (2nd mark). When they say Add, they put a vertical line on their subtraction symbol to make it an addition sign. When they say Opposite, they put a vertical mark on the negative sign in front of the 5. So the problem now looks like this: -7 + (+5) = If that second number had been a positive number, the mark they made would have been a negative sign. Because we're making that second number the opposite of whatever it was originally.

BTW, I have found that most 5th graders developmentally have a difficult time with the concept of manipulating negative numbers. They start to get it in 6th, and finally have the mental facility to work with the problems in 7th.

tiggerchyck

05-23-2008 05:28 PM

I recently talked to a math specialist and she explained it like this.

On the overhead draw a number line with positive and negative numbers. Then make a character (I liked to cut out a person I printed off the computer and put on an oiverhead so the students can see which way he is facing).

So, take the problem given 7 - (-10)

Have the character start at 7. Since, the next number is a negative number, have your character facing the negative side of the line (to the left)

Okay... so explain to the students that every time you add a number, your character takes a step forward and everytime you subtract, he steps backward. Therefore, since it is subtraction, the character then steps 10 steps backwards landing on #17.

Let me try another problem. -4 -(-6)

The character starts on -4; then, since the next number is a negative, the character faces to the left. Finally, since you are subtracting, the character takes 6 steps backwards landing on 2.

I did this with a fifth grade class and the students really understood. I also had the children act this procedure out and they really got it. I hope this helps and doesn;t confuse you. Let me know if you have any questions.

hazeleyesinnc

05-21-2008 09:59 AM

Hey Gang,

I was given this strategy by a co-worker this year. LCO- take the problem -7 - (-10) I always have my students put the last negative number in (). Leave the first number -7 change the sign + and do the opposite for the next number. -7 + 10= 3. They have to write LCO on their papers and then rewrite the problem. If they practice it enough ....they will get it. Hope this helps.

countryteach

05-21-2008 09:04 AM

My problem is when you have a problem like: -7 - -10. I don't understand how to teach them what to do. I found a site that said to have them do the opposite and switch the minus to a plus and the second negative to a positive, so then the answer would be +3. I can see my fifth graders getting so confused. Is there a way that is easier?

Mrs. Walker

05-21-2008 08:32 AM

I teach my 6th graders this way:

First you have to make the problem an addition problem by changing the minus to a plus and changing the sign of the last number. For example, 5-6 now becomes 5+ -6. THEN,

If the signs are Different, find the DIFFERENCE between the two numbers.
If the signs are the Same, find the SUM of the two numbers.
Pick the sign of the larger number for your answer.

Hope that helps!

countryteach

05-21-2008 05:43 AM

I am having a very difficult time getting the students to understand adding and subtracting integers. Does anyone have a great idea for this? Please help.