[Boost-users] [Math] Bug in example code / doc (Binomial Distr.)

Subject: [Boost-users] [Math] Bug in example code / doc (Binomial Distr.)
From: Ralf M. (rm_at_[hidden])
Date: 2009-08-31 18:56:23

On p.66 (Binomial distribution, "Binomial Quiz Example") of the
Math Toolkit pdf-file, and also at http://www.boost.org/doc/libs/1_40_0/libs/math/doc/sf_and_dist/html/math_toolkit/dist/stat_tut/weg/binom_eg/binomial_quiz_example.html 
it is written:

 "Probability of getting exactly 11 answers right by chance is 2.32831e-010"

I think this is wrong. It rather should be one of these below:

 "Probability of getting exactly 11 answers right by chance is 0.000247132"
or
 "Probability of getting exactly 16 answers right by chance is 2.32831e-010"

I have'n checked the underlying source code of this yet;
ie. maybe it is only a doc error...

And this code there seems IMHO to be problematic too:
"
int questions = 16; // All the questions in the quiz.
int answers = 4; // Possible answers to each question.
double success_fraction = (double)answers / (double)questions; // If a random guess.
// Caution: = answers / questions would be zero (because they are integers)!
binomial quiz(questions, success_fraction);
"

Shouldn't the second param not simply be the constant p of each item, ie. here 0.25,
even if # of questions is set to a different value, for example 32 ?
Because 32 / 4, as done above, wouldn't be 0.25 anymore...