Rounding off numbers

Published 01-14-2005 5:02 PM | jokiz
Back in grade school (Third Grade if I can remember it correctly), rounding off a number which is exactly in between (halfway) follows the “nearest even rule”.  Rounding off 0.5 and 1.5 to their nearest units digit gives:
2.5     ->      2
3.5     ->      4
After that, perhaps in high school, a new rule was presented and applied, numbers exactly in between should always be rounded up

2.5     ->      3
3.5     ->      4

Since then, until college, the “halfway always rounds up” rule was always applied.  When my officemate asked me a basic question about the Round function, I was able to dig up issues on rounding numbers in the public newsgroups.  I discovered that the nearest even rule is actually the Banker’s Rounding as they call it, which is a standard for rounding off numbers (since statistically, it gives a better balanced approximation).  The other one, which engineers are familiar with is the Arithmetic Rounding.  In programming (particularly in .NET), the Banker’s Rounding is in effect and if one needs the Arithmetic Rounding, one should implement their own custom function.  I also found out that MS Excel is using Arithmetic Rounding by default.

Reference:
MSDN KB on Rounding

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Comments

# Brian said on November 15, 2006 6:03 AM:

I have a problem with rounding off decimsl numbers in MS Word after I have mailemerged it from Excel to Word. I've changed the datatype to General in Excel and the same problem persists. Any advice, please?

# Penny said on September 13, 2007 8:18 PM:

I am finding it harder and harder to explain how to round off numbers to my daughter who is in the 3rd grade, she just doesn't understand, do you have a simple way to explain to her?

# kymistry said on September 24, 2007 7:43 PM:

in your 1st example. i'm confused???? if it is a 0.5 you round down or up. because the 1st example has no continuity. please help/advise????????????

thank you

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