Incorrectly calculating of percentages

[Maxim Taranov]

When adding or subtracting the percentage taken from 1, but not from the number entered.

[Yuly Nesterov (inpr1se)]

Same problem.

[Danielle Foré (danrabbit)]

OP, can you post a sample equation? I'm unsure I understand how to reproduce the problem.

[Maxim Taranov (png2378)]

For example, "100+25%=100.25" or "100+100%=101".

[Marvin Beckers (embik)]

I still do not understand this bug report, sorry. "100 + 25% = 100.25" is expected behaviour. 25% IS 0.25 - if you want to add 100% and 25%, type in "100% + 25%".

[Leonid Semenov (s3rious)]

Marvin, nope. This in not completely true.
25% is 0.25 only if it’s a 25 percent of 1.
But I’m not expect it should be percentage of 1, I’m expect if be percentage of previous calculation.

Look at the Wolfram, it does calculation completely right. http://www.wolframalpha.com/input/?i=100+%2B+5%25
It took 100, get 5% of 100 (5) and sum it.

More coplexly. http://www.wolframalpha.com/input/?i=100+%2B+50+%2B+5%25
It took 100, add 50 to 100, and sum the 150 and 5% of 150 (7.5).

Got it?

[Marvin Beckers (embik)]

Well, looks like every other calculator is working that way, thanks for finally clarifying that bug report. I honestly did not know about that before. Marking this bug accordingly.

[Leonid Semenov (s3rious)]

Marvin, Nope.
Google calculates almost fine. It can calculate simple stuff, but fails on complex.

Here:
https://www.google.com/search?newwindow=1&q=100%20%2B%2050%20%2B%205%25&rct=j

It calcs like this: 100 + (50 + 5%), but it should do it this (100 + 50) + 5%.

Also windows calc do it fine, and os x too, but just because them are "step-by-step" calculators.

[Marvin Beckers (embik)]

Okay, stop confusing me now. Is this bug valid to you or not?!

[Leonid Semenov (s3rious)]

Marvin. Totally valid.

[Brandon (brandonbocklund)]

I don't think this is valid.

    Google gives the following calculations:
        10 + 5 - 10% = 14.5
        10 - 10% + 5 = 14

    Wolfram Alpha gives the following:
        10 + 5 - 10% = 13.5
        10 - 10% + 5 = 13.5

    web2.0calc.com gives the following:
        10 + 5 - 10% = 13.5
        10 - 10% + 5 = 14

    Excel gives the following:

        =10 + 5 - 10% = 1490% = 14.9
        =10 - 10% + 5 = 1490% = 14.9

    I don't have a Ti calculator on hand, but I'm not sure if it would interpret the % anyways.

[Leonid Semenov (s3rious)]

Brandon, it seems web2.0calc.com is only valid one.
Second calculation must be interpreted like a (10 - 10%) + 5, when 10% is 10% out of 10.

I've does not really understand why wolfram calc the (10% + 5) with higher priority, but thats wrong.

[Brandon (brandonbocklund)]

It seems to me that it's an unsafe assumption to use % as anything other than a decimal (e.g. 10% = 0.10).

E.g.

x - 10% is interpreted as x - x*10%, because 10% should always be assumed as 10% of 1 mathematically. Just like x is really x*1.

[Djax (parnold-x)]

Mathematically exact it is like Brandon said.

But for most use cases maybe the other behavior is useful when it is not leading to false results.

[xapantu (xapantu)]

Ok, let's sum up:

10 + 10% = 11
10 + (10% + 5%) = 10 + (15%) = 11.5 OR 10 + (10% + 5%) = 10 + (10% * 1 + 5%) = 10 + (0.1+5%) = …
(10 + 10%) + 5% = …

10 + 10% = 10 + 1*10% = 10.1

Seriously, 10% = 0.1, period.

Suggestions welcomed, but as far as I can see, what is proposed here is not possible.

People got to learn maths, sorry :P

[Lewis Goddard (lewisgoddard)]

Related: http://math.stackexchange.com/questions/1435641/how-should-an-application-handle-the-addition-of-a-percentage

[lexsurkov (lexsurkov)]

I offer in case of entering the expression of 10-10%, a message 'not a valid expression ". If I need to subtract 10% I have to write a 10-10 / 100. I think that this is correct and understandable.