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Re: 34.123*89 = 3036.95 (3036.947)

• To: mathgroup at smc.vnet.net
• Subject: [mg47958] Re: 34.123*89 = 3036.95 (3036.947)
• From: ancow65 at yahoo.com (AC)
• Date: Sun, 2 May 2004 04:50:58 -0400 (EDT)
• References: <c6s538$pkf$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

thomas-k-schulz at t-online.de (Thomas Schulz) wrote in message news:<c6s538$pkf$1 at smc.vnet.net>...
> I am a NewBe - and i dont understand the Result.
> Mathematica says that 34.123*89 = 3036.94699999997 but its 3036.947...
> How can i change this?
> 
> i use a IBook (G4) with Mac OS X.
> THX
> Thomas

Thomas,

In my opinion, which definitely is not shared by mathematica
developers, you pointed to a design problem. By default, Mathematica
treats decimals as approximate numbers no matter what you might think.
One way to get what you want is to use rationals and take the
numerical value afterwards.
 
(34123/1000)*89 // N 

You can also use 'elegant' tricks like the following one.

ToExpression[StringTake[ToString[34.123*89], 7]]
=> 3036.95 

Because you said that you a beginner, I am warning you. Don't play
with trailing zeros.

ToExpression[StringTake[ToString[34.12300000000000*89], 7]]
=> 3036.95  

ToExpression[StringTake[ToString[34.1230000000000000*89], 7]]
=> 3036.94

I am being sarcastic here.

I refer you to a current thread on mathgroup 'Re: bug in IntegerPart
?' that discusses the core of your problem. There were also number of
tasty discussions on the subject in past on math group and
sci.math.symbolic.

Cheers,

AC