Too late to edit, but I just realized I had a brain fart. Even so, the last part is relevant.
I think this is the key: it’s only consistent with the multiplication (and division I guess). That’s purely what it’s designed for. That it fails to work how one would expect addition of a % to work would probably have been irrelevant to the original programmers - because I bet the calc app was just ported over from an old calculator.
As **jragon **noted above, it’s how programmers think. Clearly programmers are strange and curious folk. I should know; I am one.
Normal people, however, are less likely to want their calculators to behave like this, and more likely to want them to give the increase in percentage based on the original value (i.e. 100 + 10% = 110). I think all desk calculators behave this way, as do all the Casio scientific calculators that I’ve owned.
This is almost exactly what I was going to say.
My calculator is a Casio fx-991MS
This is simple: to add 8.25% tax to a sum, enter sum X 1.0825 = ____
Works every time.
ahh- beaten to it-
Interesting. I should go home and check, in case my memory is playing me false. Windows calculator gives me 110, and the scientific mode doesn’t have a % button. Apparently in scientific mode you’re too cool to need a % button.
Go to this page at CalculateNow.biz and enter :
Selling price : 108.99
Cost price : 100
Click Calculate and you will get :
Gross Profit (%) : 8.25 %
I guess it makes sense if the calculator has some kind of switch to select markup vs. gross profit mode, though that still seems odd to me. I’m having a hard time imagining a situation where you know the original number and not the final, and want to work with gross profits. I can see having original+markup and wanting the final price, or having the final price+gross profit and wanting to calculate the original number, but other combinations sound less useful.
Anyway, as others say, just avoid the percent key and use straight decimals. No ambiguity.
I’ve never done it the way awottokat does it. The way I did it on my ancient Casio calculator was: 100 * 8.25% + = and got the correct result. When I did it as 100+8.25%, I got the same result as he/she did.
I guess from the responses, people’s calculators can function differently from each other, but I tried using the % on two different calculators, one I bought in the 80s, and the other built into my iPhone and got identical results.
Taking 8.25% of 100, and adding it to 100, I entered
100
+
8.25
% key
8.25 (shows on display)
108.25
Taking 8.25% of 67 and adding it to 67, I entered
67
+
8.25
% key
5.53 (shows on display)
72.53
Both calculators gave the same correct answers in each case.
So, although not all calculators treat percentages in the way awottokat was looking for in the OP, at least a few do. I guess it’s best not to depend on it for consistency, but better to just use a decimal all the time since different models of calculators can vary widely in some of their functions.
This is why I never use the % button on a calculator. I already know what I want, so I just calculate it.
To use the % button, I’d have to figure out how it works. Then remember it for the next time. Then hope the next calculator I use works the same way.
Huh. I thought all calculator % keys did this. I always thought it was pretty useless as a kid, but it’s what I’m used to.
I know this thread is old, but let me explain why I think this way. The percent symbol has a meaning, there’s a difference between 10% of x (as in “10% of my 20ml of alcohol is Vodka”) and 10% off x (as in “this fabulous blouse was 10% off its normal $20 price at Macy’s”).
Former:
10% * x
Latter:
x - (10% * x)
Now, you might say, “but x - 10% * x” is intuitive, it’s what I think of when I say x - 10%!" Well, yes, but now you’re defining the percent key to have completely different meanings depending on context. That’s not something you usually want in a calculator.
Even as a non-programmer, I want my calculator keys to be as unambiguous as possible, I want to know that the ->Frac button will turn a rational decimal into a simplified fraction every time. I don’t want to have to guess on a test, or while doing life-saving ballistics calculations, that the percent key MAYBE does this or that. Even if you still want it to be context dependent, what does it do in the case of y + 10% * x? Sure, you can define rules (such as multiplication takes precedence by PEMDAS so it makes it operate as .1), but given there’s no standard rules for this behaviour it introduces even more guesswork.
This leaves only one real option – 10% = .1; which does make it a rather useless button, but it’s the only uniform option that really makes sense to me.
Like I said above, I can see a reasonable need/desire for a button such as x + 10%OF which is a macro for x + 10%*x, but I think making the default percent key assume that makes the user do too much guessing.
Granted, according to this thread making it NOT do that is already making the user do too much guessing.
I hate the percent key on the calculator. And I hate the percent format in Excel. I never use either.
I never noticed before this thread, but my HP 12C (I think 12C; label fell off) has both a % key and a delta% key. My wife’s 11C has them too.
A <Enter> B % gives B% of A. i.e. it gives B * A / 100
A <Enter> B delta% gives the percentage change from A that gets you B. i.e it gives you 100 * (B-A)/A.
(For those who don’t know, HP 12C uses Reverse Polish Notation. i.e., it has an Enter button, and no = button. So to add 2 and 3, I’d press 2 <Enter> 3 +. The result 5 would be on the display.)
I’ve always understood that calculators that can calculate percentages the way we’re talking here (100 - X% or 100 + X%) are called “sales calculators.” They’re designed to assist people in the sales industry to easily calculate margin, sell price, etc.