Rounding decimals.

SunlampVexesEel · Post by **SunlampVexesEel** » Fri Jul 10, 2009 8:49 am

Annoying video...

http://www.videojug.com/webvideo/how-to ... al-in-math

dadofkent · Post by **dadofkent** » Fri Jul 10, 2009 8:55 am

SunlampVexesEel wrote:3.25487

Rounded to 2 dp is 3.25

Imagine a number line... 4 is less than 5.. clearly rounds down.

Moving from the right, accumulating 'rounding' is clearly bogus.

My view also.

essex-mum18 · Post by **essex-mum18** » Fri Jul 10, 2009 9:09 am

My answer would be also 3.25. Same rationale as the last 2 posters.

yoyo123 · Post by **yoyo123** » Fri Jul 10, 2009 9:28 am

3.25, same reason as hermann, the remaining numbers are less then halfway so you round down

Wallasey · Post by **Wallasey** » Fri Jul 10, 2009 10:42 am

You only look at the one digit to the right of the place you want to round to. All the other digits further to the right are irrelevant because their value is so much less in comparison (tenths, hundredths etc). If the number is 01234 you don't change the original. 56789 are all half or more, so the last decimal is rounded up.

This makes the answer 3.25 because the next number is a 4.

Looking for help · Post by **Looking for help** » Fri Jul 10, 2009 10:49 am

I agree 3.25 , if it was to 1 dp it would be 3.3 (because of the 5, which I think you always round up), 2 dp is 3.25 (because 4 is less than 5 -halfway point)and 3 dp is 3.255 (because of the 8-more than halfway)

LFH

KenR · Post by **KenR** » Fri Jul 10, 2009 11:17 am

The following article explains that the answer for a single rounded number is 3.25

http://mathforum.org/library/drmath/view/58915.html

The problems tend to arise with scientific experiments where progressive rounding can result in significant rounding errors.

So often you are instructed to work out you answers to a number of decimal or significant places(say 3) and then round your final answer to say 2 decimal places

So in this case even if the final answer was required to 2 decimal places you might use 3.255 in your interim calculations which would round down to 3.26

You just need to have a clear strategy

SunlampVexesEel · Post by **SunlampVexesEel** » Fri Jul 10, 2009 11:30 am

KenR wrote:The Excel ROUND function however thinks it's 3.25 but I think it's wrong.

Actually Excel has a number of rounding functions. ROUND is defined as round nearest which is the normal notion of to 2 d.p.

Code: Select all

3.25487	VALUE			
				
	=ROUND(VALUE,2)			                3.25
 	=ROUNDUP(VALUE,2)			                3.26
	=ROUNDDOWN(VALUE,2)			3.25
	=MROUND(VALUE,0.01)			3.25

2010 mum · Post by **2010 mum** » Fri Jul 10, 2009 12:47 pm

Rounding to 2 decimal places: 3.25487

My answer is 3.25.

Reason:
Principle of rounding, states 5 as the mid point. Less than or = 5, stays in the same state (ie, if it is 3. 254, it remains as 3.25 as 4 is not greater than 5). Greater than 5, the number is rounded to the next increment (ie, if it is 3.256, the 5 increases by 1, as 6 is greater than 5, in this instance the answer would be 3.26).

I hope this helps.

thanks.

Bexley Mum 2 · Post by **Bexley Mum 2** » Fri Jul 10, 2009 12:56 pm

I'm glad I read this thread. I'd always assumed that you just rounded up from the right. But it makes sense, if you are rounding to 2 decimal places, to just look at the 3rd. I'm persuaded that it's 3.25!