HP 12C Permutation and Combination

[Dieter]

(08-17-2017 12:25 PM)Gamo Wrote:  I decided to calculate manually this way because of the rule of operation that must start from the inner most parentheses first

First of all, you do not have to start at the innermost parentheses.

(08-17-2017 12:25 PM)Gamo Wrote:  and I have no choice to reverse the division by using 1/x since the problem start from the denominator portion of the fraction.

There always is a choice in RPN. Instead of first dividing "the wrong way round" and then correcting this by [1/x] you can simply use [x<>y]. If you really want to start with the denominator (which does not make much sense here), and after the numerator 25! has been calculated afterwards, simply press [x<>y] [/]. This way numerator and denominator are swapped.

(08-17-2017 12:25 PM)Gamo Wrote:  I believe that calculate this way give more accurate result.

I do not think so. ;-)

Not convinced? Just try a very simple example like P(7, 1). Or P(13, 8). Or P(11, 8). Or... Whether the one or the other method causes more or less roundoff errors depends on the two arguments and how well the intermediate results happen to round to 10 digits. Just the way it is with most finite precision calculations.

Dieter