https://howardat58.wordpress.com/2018/05/25/subtraction-what-exactly-is-it-bonus-is-8722/

]]>Good ideas.

]]>This is kind of how I teach it, but math is not my subject area, science is. But I sub math sometimes and help students who show up after school with their math.

Here’s how I approach it, admittedly not as introductory concepts.

You have to start thinking of these problems on a higher level than “add and subtract.” You are combining 2 (or more) numbers to find a value. Don’t look at the + and – signs as telling you to add or subtract, attach them to the number after them as positive x or negative x.

So -5+3= is -5 with +3. If both numbers are the same sign: add. If the numbers are different signs: subtract (remember “find the difference?”). The sign of your answer will be the same as the bigger number (higher absolute value).

I actually show them on a number line (moving right 2x, moving left 2x, or moving 2 different ways). But that is the basics of it.

]]>Common Core was right to utilize number lines, for sure.

The visualization is helpful in making students more sure of themselves, whatever the calculator might say. It actually works better as subtraction than adding a negative, judging by how the students’ eyes develop a look of skepticism.

The concept of subtraction and the need for precision in which number is first has been forgotten by some of the same students who can write a fraction correctly, then proceed to put the numbers in the calculator in reverse order, plus some others. Luckily, distance can be dealt with and used even with bad sense of direction.

No, that’s how we teach it.

]]>(It does look similar to the “rub out the minus” approach that some students like so much!).

My approach is to separate the “and” from the signs, and write it like this:

a – b is …. +a “and” -b

and then do the combination

So we get as well

+a “and” -(-b)

as

+a “and” +b

which is conventionally written a + b

Have fun with this !

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