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Rounding Millions


Date: 08/24/97 at 16:15:03
From: Jerry Tuttle
Subject: Question on Rounding

Dear Dr. Math,

I guess I have never understood the rules about rounding of numbers.  
Of course 5 or greater rounds up and 4 or less rounds down, but how
many significant digits does this affect?  

I amlooking at the number 308,499,000 and I want to round it to the 
nearest million; is it 308 million ignoring the 99, or is it 309 
million?

Thank you.


Date: 08/25/97 at 09:22:30
From: Doctor Jerry
Subject: Re: Question on Rounding

Hi Jerry,

One way of thinking about rounding is to imagine a number line.  Since 
you want to round to the nearest million, imagine a number line:

----------|----------|----------|----------|----------|
         306        307        308        309

The vertical segments mark the numbers 306 million, 307 million, 308 
million, and 309 million.

Now imagine plotting the number 308,499,000.  I'll try to indicate its 
position below, with a *.

----------|----------|----------|----------|----------|
         306        307        308   *     309

It's a little bit closer to 308 than 309 (308,500,000 would be at the 
middle point).  Hence, if you round to the nearest million, you'll get 
308,000,000.

-Doctor Jerry,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/   
    
Associated Topics:
Elementary Large Numbers
Elementary Place Value

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