The statement of the problem is flawed. Since @numbers is sorted numerically, @small = sort {$a <=> $b } @small should be sufficient.

Unfortunately, his statement of what @small should be doens't seem to match the problem statement, in that @small actually contains 80.9, but what he says @small should be does *not* contain 80.9 - what are we to make of that?

Anyhow, if we assum that @small is a subset of @numbers, which the AM wants ordered the same way as @numbers, and for some reason, sort() is not the solution, the following would seem to work for any ordering for @numbers.

my @numbers = qw(76.8 77.0 77.2 77.4 77.6 77.8  78.0  
                78.2 78.4 78.6  78.8 79.0 79.2 79.4 
                79.6 79.8 80.0  80.2  80.5 80.7 80.9 81.1);
 
my @small = qw(78.6  78.8 79.0 80.9 77.0);


$s{$_}++ for @small;

@ordered_small = grep { exists $s{$_} } @numbers;

# demo code below:
print "@ordered_small\n";

@numbers = reverse @numbers; 

@ordered_small = grep { exists $s{$_} } @numbers;

print "@ordered_small\n";
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Update: On closer reading, the problem statement is hopeless. How are the numbers in small "selected", and what makes the first or last (or any other) number in @small "wrong"?

--Bob Niederman, http://bob-n.com