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Re: I need help in the order of my teaching!!!
Posted:
Apr 10, 1998 8:51 AM
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I am not a classroom teacher, but here is what I do with my college
students in a math for elementary teachers class. I usually look at
rounding (and other ideas) in a base-7 system.
I set up a imaginary situation where you are walking along the street.
All the houses on this street are on one side of the street and they are
numbered consecutively. So, for example,
300, 301, 302, 303, ..., 364, 365, 366, 400, 401,...
Furthermore, there are bus shelters in front of every '100' houses. Then
I pose the question, suppose you are walking along this street, and you
are in front of the house number 326/351/342/335 when it started raining.
The question is, to which bush shelter would you run for.
Usually 326 and 351 are easy. 342 and 335 cause them to think a bit more
because the 'rules' they learned don't quite work out. Basically, they
conclude that they have to figure out the distances to each shelter. Then
we look at how we can come up with a set of rules that will allow us to
decide this quickly. Maybe Patrick can adopt this to 2nd graders.
Now, an editorial comments. I have seen this idea of rounding introduced
with rounding to the nearest tens. I tend to believe that this idea
should be introduced with the question that askes students to round
numbers to the nearest (at least) hundreds. The problem with rounding to
the nearest tens is that '5' is in the middle - as students try to
establish a rule. I have seen many students who simply say 5 is rounded
up just because. However, when you look at larger number, say rounding to
the nearest hundreds, there are 10 numbers in the interval with 5 in tens
place: *50, *51, *52, *53,..*58, *59. All of these numbers except *50 is
indeed closer to the larger hundreds. So, it does make sense, if you were
to create a rule based on the digit next to the place you are rounding to,
to make 5 round up. It is still true that *50 is still in the middle, at
least this fact 9 out of 10 numbers should be rounded up (and none should
berounded down) seems to make it very reasonable we 'arbitrarily' round up
the very middle number.
Tad Watanabe
Towson University
Towson, Maryland
On 9 Apr 1998, patrick wrote:
> I need to review skip counting , introduce rounding , grouping
> (pre-multiplication), and place value at the 2nd grade level. Should I
> use a 100's chart to show skip counting and rounding and then use the
> yellow ones, tens, and 100 squares to show place value and grouping.
> First, manipulatives and then numbers. I need an experienced teacher
> to give me some advice. Thanks Pat
>
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