I think you need rand(100) for 0-100, excluding 100. Using that, how about something like this: 
use strict;

# five options, with 50%, 25%, 10%, 10% and 5%
# chances respectively.
my %hash = ( option1 => 50,
             option2 => 25,
             option3 => 10,
             option4 => 10,
             option5 => 5);

# get rand num - may want to seed it first though :)
my $rnd_num = int(rand(100));

my ($total,$key);

# cycle through hash values
for (keys %hash) {

  # keep running total
  $total += $hash{$_};

  # keep going until rand num exceeded
  next unless ($total >= $rnd_num);

  # then set this as value selected and stop loopin
  $key = $_; last;
}

# randomly selected key is...
print "$key selected\n";

[download]

cLive ;-)

PS - If total isn't always 100, change the 100 in the rand as follows: 

my $value_sum = eval join '+', values %hash;
my $rnd_num = int(rand($value_sum ));

[download]

In reply to Re: Per cents and Probabilities by cLive ;-)
in thread Per cents and Probabilities by dimmesdale

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