You need two passes, one to count the total number of words, the second to pick a word based on the rand value. 
use strict;
use warnings;

my (%h, %c);

while (<DATA>) { chomp; @_ = split / /; $h{$_[0]} = $_[1]; }
$c{weighted(\%h)}++ for 1..1000;
print "$_ : $c{$_}\n" for sort {$c{$b} <=> $c{$a}} keys %c;

sub weighted {
    my ($p, $c) = shift;
    $c += $_ for values %$p;
    $c = (int rand $c) + 1;
    for (keys %$p) {
        return $_ if ($c -= $p->{$_}) <= 0;
    }
}

__DATA__
gamma 7
beta 6
epsilon 3
alpha 2
delta 1

[download]

In reply to Re: "Scalar found where operator expected", references by TedPride
in thread "Scalar found where operator expected", references by jjohhn

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.