1. ## Strange rounding

Hi there,

I have this problem with naming the following strange kind of rounding:

- 2,51 = 2,55
- 2,56 = 2,60
- 2,47 = 2,50

So this is rounding to two decimal digits, but strange one, when I have only 0 or 5 in the second decimal place. Have you heard of a name for anything like this, and if not, do you have any idea how to explain this in one easily understandable sentence?

Thanks,
Nyggus

2. ## Re: Strange rounding

In mathematics, this is how rounding goes:

-2.51 - when you have to round it to the closest tenth, what is next to the tenth digit on the right side - let it be denoted by x (hundredth digit) - has to be 0. You add one to the tenth digit if the hundredth digit is 6≤x≤9 and make the tenth digit even if x=5. If 0≤x4, then the tenth digit remains intact.
In our case the hundredth digit is 1 --> 2.50

Of course you can invent other rules for rounding:
rounding of the last two, or the tenth and the hundredth digits to the higher of the two nearest multiple of five.

2.51 --> 51 (50; 55); 50≤55 --> 2.55

(I have an MSc. in maths)

3. ## Re: Strange rounding

Originally Posted by nyggus
Hi there,

I have this problem with naming the following strange kind of rounding:

- 2,51 = 2,55
- 2,56 = 2,60
- 2,47 = 2,50

So this is rounding to two decimal digits, but strange one, when I have only 0 or 5 in the second decimal place. Have you heard of a name for anything like this, and if not, do you have any idea how to explain this in one easily understandable sentence?

Thanks,
Nyggus
You are "rounding up to the nearest 0.05".
svartnik explains it well, but he didn't mention 'rounding up' and 'rounding down'.
Obviously you are demonstrating 'rounding up' otherwise 'rounding to the nearest 0.05, or hundredth' would make 2,56 => 2,55.*
Note also that in English, we a period . for a decimal place, and a comma for a divider of large numbers.
1,234.56
1,987,654.32

* This is important in Australia for money. We no longer use coin denominations below 5 cents, but individual items can still be 57 cents, etc. Rounding is done to the nearest 5 cents - whether that is up or down. If your grocery bill comes to \$15.97 you pay \$15.95; if it's \$15.98, you pay \$16.00.
This meant that if you wanted \$15.00 worth of petrol, you'd try to pump out 15.02 worth. But now that petrol costs about \$60 to fill a tank, the extra few cents of free petrol is hardly worth it.

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