Dear Monks, I want to calculate the propability to get side 1 at least k times, tossing a coin n times.

The following code works fine with numbers up to about 150 but when I use numbers above, I get the result -1.#IND

Is there a better way to solve this problem?

#!/usr/bin/perl -w

$coin_toss=1000; # =n
$toss_side1=60; # =k

$total_p=0;
foreach($toss_side1..$coin_toss)
    {
    # calculate factorials
    $n_fac=fac($coin_toss);
    $n_minus_k_fac=fac($coin_toss-$_);
    $k_fac=fac($_);
    
    # calculate propability for getting side 1 exactly $_ times
    $partial_p=($n_fac/($n_minus_k_fac*$k_fac))*(0.5**$_)*(0.5**($coin
+_toss-$_));
    
    # add propability to total propapility
    $total_p=$total_p+$partial_p;
    }
print"Propability to get side 1 at least $toss_side1 times tossing a c
+oin $coin_toss times: $total_p\n";
system("pause");
exit;

# subroutine for calculating factorials
sub fac
    {
    $_[0]>1?$_[0]*fac($_[0]-1):1;
    }

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In reply to Calculate propabilities without recursion? Coin toss. by Microcebus

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