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Topic: [math-learn] significant digits
Replies: 16   Last Post: Feb 28, 2002 7:49 PM

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Suzanne Alejandre

Posts: 113
Registered: 12/3/04
Re: [math-learn] significant digits
Posted: Feb 28, 2002 4:39 PM
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Lin,

>But all you want to know is if the speed more than 25 mph or less than 25mph.
>Why round off at all? In fact you could convert 25 mph to seconds per (1500
>meters) and just look at the times.
>
>What are you asking?


I'm asking "if" this is a case of dealing with significant digits.
From what Ed Wall replied earlier, it sounded as if he understood
that I was asking if it is "correct" to state the skater's or
runner's speed only using 4 or 5 digits (and therefore, rounding
off). I thought that his explanation with the +- error was the
closest to what I was talking about. As other people have replied,
I've tried to explain why I rounded off at that point. So, I think
the question that I actually had, got a little lost.

From what I understand so far, and best explained by Ed, it is
important to consider significant digits in this case even though
it's not something like Ron Ferguson explained. One place that I read
in the Ask Dr. Math archives was this explanation by Doctor Peterson:

Rules for Significant Figures and Decimal Places
http://mathforum.org/dr.math/problems/ashley03.23.99.html

To be honest, when I first wrote the problem and as I was mentoring
the problem I didn't really think much about significant digits. I
had rounded off the numbers thinking that all of those digits weren't
necessary. What happened, though, was that if you work the bonus
question a certain way and IF you have rounded off too much your
answers are inaccurate. That all led us to think more about what
really are the significant digits that should be used in this problem.

Maybe others wouldn't have thought this important to teach at a
middle school level? Should all of the numbers of the speeds be left
in their entirety?

Suzanne

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