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Rounding Numbers


Date: 9/24/95 at 10:13:13
From: Anonymous
Subject: Round up or down?

I'm Kyrene de la Sierra and I'm in 3rd gradein Phoenix.  I want to ask about 
rounding numbers.  Let's say we have to round to the nearest 10's.
11,12,13,14,15,16,17,18,19...  What do we do with 15? It's right in 
the middle.  Not too small, not too big, just right.


Date: 9/24/95 at 12:35:48
From: Doctor Jeremy
Subject: Re: Round up or down?

Usually, the 15 would be rounded up to 20.

Rounding up is good in some ways.  One time you might round numbers is when
you measure something.  You never measure something just right.  Suppose
I measure something and get 350-something inches.  It's that something
extra that matters.  It might be 351 inches or 353 inches, so there's a
good chance it'll be a bit closer to 400 than 300.

Another way to look at it is that you've got the 10 digits, and you want to
know where to round each of them.  A logical way to do it is round the first
5 down and the rest up.
The first five are 0,1,2,3, and 4.
The last five are 5,6,7,8, and 9.
So you divide rounding up and down fairly in the middle.

I've seen rounding done other ways, but if you don't know which way to
round, you round up.

-Doctor Jeremy,  The Geometry Forum
    
Associated Topics:
Elementary Place Value

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