Math Is Fun Forum

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Rounding numbers in recent additions

In "recent additions", I read about "rounding numbers".
The only word I would change is the one that says,
"it is all about fairness", when talking about why
the digit 5 is rounded up.  I think it would be more
fair to say it is typically agreed upon that 5 should
round up.  There are some times when 5 may round
down, but this is not the normal way to do it.

Finally, 5 is exactly halfway, so there is no fairness.
Teams with an unfair zero on a team is not fair.

Sorry we already talked about this before, but I couldn't resist mentioning it again.

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igloo myrtilles fourmis

MathsIsFun

Administrator

Registered: 2005-01-21

Posts: 7,713

Re: Rounding numbers in recent additions

Yes, I need to write a much lengthier article about methods of rounding. Floor, ceiling, rounding 5 up on even or odd, etc.

It really is about "horses for courses", but the "5 up" method is simply the most common and agreed-upon method.

I guess you really need to think about your data before you decide what method to use.

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"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

George,Y

Member

Registered: 2006-03-12

Posts: 1,379

Re: Rounding numbers in recent additions

0.0 0.1 0.2 0.3 0.4  5 numbers
0.5 0.6 0.7 0.8 0.9  5 numbers
fair

0.00 0.01 ... 0.49 50 numbers
0.50 0.51 ... 0.99 50 numbers
fair

0.000 0.001 ... 0.499 500 numbers
0.500 0.501 ... 0.999 500 numbers
fair

so the rounding can be inferred (imagined) as fair.
when talking about infinity, you can only infer and define.

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X'(y-Xβ)=0

Ricky

Moderator

Registered: 2005-12-04

Posts: 3,791

Re: Rounding numbers in recent additions

I guess you really need to think about your data before you decide what method to use.

That could be a very large pitfall though because people can choose their rounding method to make their data fit better.  Although in most cases it's not going to make a big difference.

George, I agree.  The one thing people say is that you aren't rounding .0, and thus, it doesn't count.  I can't understand why though.

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"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."