[X4U] Tiger's Calculator.app no longer does percentages?

[Eugene]

On Mon, Nov 28, 2005 at 05:01:46AM CST, Kuestner, Bjoern <Bjoern.Kuestner at drkw.com> wrote:
: 
: I taught both math and physics, and for exactly the issues discussed here I
: told students to stay away from the % button.
: 
: Although % is clearly defined mathematically as 15/100, the trickery of
: using % on a calculator is a pain.
: 
: In this example some suggest that 15% should be just what it is
: mathematically, i. e. 15/100, which is what Tiger does. Other suggest that
: the calculator should act "more intelligently" and the software should imply
: that it must be 15% of something and then figure that it has got to be 15%
: of 28.05.
: 
: But then, what if you type: 15 + 25 + 10%
: 
: Unless you use parentheses, what should the calculator assume? Some would
: say "15 + 10% of 25", others would say "10% of 15 + 25".
: 
: The only way out of this mess is to not use the percentage button and
: clearly tell the calculator what you want to do:
: 
: 28.05 * 1.15 or 28.05 + 28.05 * 15%
: 
: and respectively
: 
: ( 15 + 25 ) * 1.1 or 15 + 25 * 1.1

Percentages only make sense in the context of another number.
When doing the math, percentage is always multiplied to that
other number.  It makes no sense by itself.  When doing the
logic, when you see "percentage", always ask yourself
"percentage of what?"

So in your example, you first step back and ask "10% of what?"
If it's 10% of the sum of 15 and 25, then the correct math is
simple:

	(15 * 25) * 0.10

As for the percentage button on a calculator, its order of
operation should be equivalent to other function buttons.
For example, when you hit the x^2 button or the sqrt button,
the calculator immediately takes the number in the current
stack, performs the function, and returns the new value in
the current stack.  The percentage button is no different.

The real problem is that American children are no longer taught
how to use math as they are taught how to use a calculator....


-- 
Eugene
http://www.coxar.pwp.blueyonder.co.uk/