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Calculator Error

The calculator app that comes with the Android OS apparently has an error. I've confirmed this error with two other Moto Droids and one HTC Android phone.

In the calculator app enter:

3322.72 - 3321.92 then = and the answer is .799999

The correct answer is .80

This may seem like a minor point (.000001 error) but the answer is still wrong! Basic arithmetic operations should be a no brainer...

A Verizon service rep confirmed this error on the Droid and Eris phones he had in their call center. I wonder if 2.1 will fix this?

Does anyone else get this result?
 
mathematically, .79999 repeating =.8, if the 9 repeats forever.

to see this, write .79 repeating equals x.

10x =7.9 repeating.
10x-x =7.2 = 9 x
x=.8
there are other proofs. it's well established

perhaps the droid just appreciates the subtlety of math :)

your proof is wrong... by what you set x to be, 10x-x=7.19999... assuming it's 7.2 is assuming what you're trying to prove

the correct proof would be to take the limit of its p-adic expansion.
 
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your proof is wrong... by what you set x to be, 10x-x=7.19999... assuming it's 7.2 is assuming what you're trying to prove

the correct proof would be to take the limit of its p-adic expansion.

Oh no! another product of poor math education. Or perhaps you're using the Droid calculator?

7.999999999999999...
- .799999999999999...
=7.2

No ambiguities bub.

Consider .9999999999...=x
10x=9.99999999...
x=.99999999...
9x=9 x=1
 
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Oh no! another product of poor math education. Or perhaps you're using the Droid calculator?

7.999999999999999
- .799999999999999
=7.2

No ambiguities bub.

Consider .9999999999=x
10x=9.99999999
x=.99999999
9x=9 x=1

No, a product of a math degree. First of all, don't appreciate the condescending attitude. Second, I would be more than happy to show you the fault in your logic.
 
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Yeah, I thought this was pretty funny as well - it's definitely a programming problem as the error occurs across different OS versions and hardware platforms.

I came across this error by chance while balancing my check book and when I came up with more than two digits after the decimal point I knew something wasn't right...

Because I'm not calculating the trajectory of a rocket launch to the moon I'm not going to worry about such a small error. Even so, I'll probably get Realcalc...
 
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Not quite a calculator error but a throwback from floating point arithmetic. This is particularly common with computations in programming, e.g., you do not test for equality to zero but rather test for proximity to machine-epsilon: abs(x)<eps.

Also, the comment above about .799999... = .8 is correct.

I remember from my advanced math education (in middle school) that .799999999...=.8, although I've never heard of epsilon. But I think everyone can agree that writing it as such is bad form, and this is clearly a glitch that should be fixed. Perhaps they should hire someone smart like ubergray to fix it.

It confused me for a while when I saw that 601.1-606.3=-5.199999

To whom should one address such a bug fix request?
 
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cue the Beach Boys" "Round round round round, I cannot round..."


It isn't the Droid, it's the Droid stock gonkulator.

RealCalc gives a nice clean 0.8.

-Les

Les is right. The OP has an issue with significant figures. Since the less significant place in either of the numbers is 0.0x, any result should be rounded to that place. Of course, the really fault does lie in the calculator, but the operator has to know not to blindly use what the calculator gives him.
 
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