Donna Curry

=E2=80=94(2009)*The Math Practitioner*. Vol. 15, #2.

### Summary

For years, many of us learned that subtraction meant =E2=80=95"take away=
". We learned certain =E2=80=95tricks to handle those gnarly word problems.=
We learned to look for words such as "less", "left", "difference", or "dec=
reased by", to decide whether we should subtract or not. And, we learned th=
at when we subtract, we always take the smaller number from the larger numb=
er. [Any of us who has overdrawn on our checkbook knows that the larger num=
ber doesn't always go on top!] Our adult learners have learned many of the =
same notions about subtraction. It's important, especially for those studen=
ts who struggle with "basic math concepts", that they revisit what subtract=
ion is really all about.

In many cases, subtraction can be considered a situation in which we "ta=
ke away" something. If I had $200 in my checking account and now have $75 l=
eft, we could use subtraction to find how much I "took away". But what gets=
taken away when we compare two quantities? What gets "taken away" if the h=
igh temperature was 32 degrees and it is now 22 degrees? What gets "taken a=
way" when we talk about the difference in our ages =E2=80=93 I was born in =
1985 (I wish!) and you were born in 1979?

Nothing is "taken away" in those examples. When we look at our ages, we'=
re comparing two quantities. So, subtraction also is used to show the diffe=
rence between them. If students don't realize this, they may not think of s=
uch a situation as a subtraction problem. Whether they count up from 1979 t=
o 1985 or whether they subtract 1979 from 1985, they need to understand tha=
t comparing two quantities can be solved using a subtraction strategy.

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