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Rounding Up or Down on a 5

Date: 06/13/99 at 20:16:54
From: Pat Slaber
Subject: Rounding up or down on a 5

We are having a disagreement in our family - my children are being 
taught always to round up if the adjacent number is 5 or more. My 
husband agrees. I was taught that if the number is, say 7.5, to round 
up to the whole number it would be 8. But if the number is 6.5, you 
would round down to the 6. This is because the 5 is smack in the 
middle and if you always rounded up on the 5, things would eventually 
get inflated and the even/odd rule kind of balances this out. I notice 
in your archives that you always round up on the 5. Do I have to back 
off on this argument?

Date: 06/14/99 at 15:17:56
From: Doctor Terrel
Subject: Re: Rounding up or down on a 5

Hi Pat,

Don't back down. But let's ask the proper question here: when and for 
what purpose are you rounding numerical values? Your mention of 
"sometimes up and sometimes down" is especially useful, perhaps even 
advisable, when dealing with a long list of data, say as an accountant 
might have. There, your idea of "the even/odd rule kind of balances 
this out." makes good sense, doesn't it?

But if you only have one data point to consider, as in a measurement 
of a length (which wouldn't be exact anyway), we have to deal with a 
compromise here. Tradition the favors the round up idea - check with 
how all scientific calculators round (with their "fix" function.)

I'd say you're both right. It just depends what the situation is.

Will this bring peace to the family?

- Doctor Terrel, The Math Forum   
Associated Topics:
Elementary Fractions
Elementary Place Value

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