Your answer is good and short for the small case you need to solve now; but that method could get out of hand if you need to solve the more general problem of picking randomly from a weighted set of items. In that case, and answer similar to Gryn's would be more appropriate.

There was another thread at Biased random number selection which has information on how to optimize the selection process for speed.

But here's the most straightforward (but not necessarily fastest... and not tested) solution:

# A list of weights; initialized for your problem
my @weights = (8, 1, 1);

# Count the total of all the counts
my $sum;
map { $sum += $_; } @weights;

# Choose a random number, then find a weighted random result
my $target = rand($sum);
for (1..@weights) {
   $target -= $weights[$_];
   last if $target <= 0;
}

print "The number is $_\n";
[download]

Hope this helps. Alan