Problem with HP 17bii+

[mod220]

I am having an issue that is driving me crazy! seems so simple but I'm stumped...when I type in "11%+4%" the calculator is converting this to ".1100+.0044" - why on earth is 4% not converting to .04, and where is the .0044 coming from?
Thanks in advance!

[Dave Hicks]

The initial % is just the number divided by 100, but in the second case, it is giving you 4% of .11 since it believes you want to add [some number] plus 4% (of that number).

[mod220]

(10-10-2023 02:33 PM)Dave Hicks Wrote:  The initial % is just the number divided by 100, but in the second case, it is giving you 4% of .11 since it believes you want to add [some number] plus 4% (of that number).

thank you. I have no idea why it would do that, more importantly, is there a way to stop this? its such a basic calculation, why would it not intuitively translate to .11+.04?

[Dave Hicks]

As an RPN/scientific kind of guy, if I wanted to add 11% to 4% I would just add the 11 and 4 and ignore the symbol. Or if I intended to take the resulting percentage of some other number, then I would just shift the decimal in my head like you did and add .11 and .04. (As such, I don’t use percent keys much – if humanity had decided that perthirtyseven was interesting, then I’d use that key!)

However, I do think that bankers/businessmen/investment advisors like to speak in terms of adding 4% in the way that the calculator does it.

[Dave Hicks]

For amusement I tried a few other calculators. The RPN models always took the percentage of the preceding number in the stack. So, (clear stack) 11% -> 0 as does 4% since we’re taking fractions of zero.

The RPL machines did so as well, but with one distinction: If you start with an empty stack and enter 11%, you get the error message “Too few arguments”. So, same behavior but with an error message that would have probably alerted you that % didn’t do what you assumed. (ie: it is not a divide by 100 button.)

The only non-HP algebraic calculator I had handy was the Windows calculator (in standard mode) and I found it to be confusing.

Invoke calculator (so it’s cleared): 11% -> 0 (not too shocking but then continue on…)

5+3 = (displays 8, now press) 11% -> .88. (which is 11% of 8)

5*3 = (displays 15, now press) 11% -> .11 (which is 11% converted to decimal)

So, it has 3 behaviors of the % key??? I tried this on both Windows 10 and 11.

[mod220]

(10-10-2023 03:48 PM)Dave Hicks Wrote:  As an RPN/scientific kind of guy, if I wanted to add 11% to 4% I would just add the 11 and 4 and ignore the symbol. Or if I intended to take the resulting percentage of some other number, then I would just shift the decimal in my head like you did and add .11 and .04. (As such, I don’t use percent keys much – if humanity had decided that perthirtyseven was interesting, then I’d use that key!)

However, I do think that bankers/businessmen/investment advisors like to speak in terms of adding 4% in the way that the calculator does it.

Thanks, this is for a financial exam I'm preparing for. I know I can easily convert to a decimal before inputting, but for simplicity, it would be nice to use the % sign, as that is consistent with my studies. I am still baffled the calculator does this, I cannot see the use case why converting to 11% of 4 makes any sense at all?

[ijabbott]

(10-10-2023 06:19 PM)mod220 Wrote:  [quote='Dave Hicks' pid='178314' dateline='1696952929']
Thanks, this is for a financial exam I'm preparing for. I know I can easily convert to a decimal before inputting, but for simplicity, it would be nice to use the % sign, as that is consistent with my studies. I am still baffled the calculator does this, I cannot see the use case why converting to 11% of 4 makes any sense at all?

Because y+x% is converted to y+(y*x%), for example:

10+4% → 10+(10*4%) → 10+(10*0.4) → 10+0.4

Also x% with no operator to the left is converted to (x*0.01), for example:

11% → (11*0.01) → 0.11

Combining the above:

11%+4% → (11*0.01)+4% → 0.11+4% → 0.11+(0.11*4%) → 0.11+(0.11*0.04) → 0.11+0.0044

If you want to avoid that behaviour, use parentheses:

(11+4)% → 15% → 0.15

You can even drop the opening parenthesis in this case:

11+4)% → 15% → 0.15