Subtraction is Not Just "Take-Away"
Subtraction doesn't always mean "take-away." No
more than "cooking" means "frying."
Use
language to introduce and clarify all the different meanings of subtraction. For
example:
- I have 3 plates, I want 5,
how many more do I need?
- You have $6, if
you spend $4, how much will you have left?
-
There are 7 people in that line and this one has 3. What is the
difference?
- Waiting for the elevator, we're
on the 6th floor. If we go down 4 floors, how many more do we have to
go?
Subtraction is not just "take
away."
- How many more?
~This recipe calls for 3 cups of flour. I've
added 2 already. How many more are
needed?~
Notice that you are not "taking
away" anything in this example. In fact, you are "adding"
flour.
-What is the difference?
~Compare the store brand price of $3 with
the name-brand price of $4.~
Notice you are
not taking away anything. Calling this "4 take away 3" would be
confusing.
-Measuring
distance.
~You drove 6 miles to a friend's
house and you are on your way home and you've gone 2 miles. How many more miles
do you have to go?
Again, nothing is being
"taken away."
Posted: Thu - November 6, 2003 at 01:52 PM