```Date: Jan 7, 2013 12:36 AM
Author: Andrzej Kozlowski
Subject: Re: Precision

On 5 Jan 2013, at 08:19, Rob Ryan <tio540s1@gmail.com> wrote:> My frustration is growing. I simply want to add (for example):> 103971.66+52282.64+2998.27. These are dollars and cents and I'd like to keep the cents. But when I input that line, I get 159923. When I input: N[(103971.66+52282.64+2998.27),20] I STILL get 159923. What do I do to get 159952.57? I've used "SetPrecision", etc. with still no result.> I note that when I type 103971.66 and hit shift-return, the output is 103972. If I then type "InputForm[%]" I get 103971.66.>> There simply has to be an easy way to add these numbers - any calculator watch can do it!In this case you can simply use NumberForm:NumberForm[103971.66 + 52282.64 + 2998.27, 8]159252.57However, this approach will not always work (to understand why you have to first understand that Mathematica's approximate reals are not what you probably think they are)A much more reliable way is to do such computations using exact numbers. This will never give you a wrong answer: QuotientRemainder[10397166 + 5228264 + 299827, 100]{159252, 57}If you don't like this, you would be better off using a calculator watch.Andrzej Kozlowski
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