Sort the indexes and apply your operations in that order without actually changing the ordering of the array:

#! perl -slw
use strict;

my @array = (2.5 ,4.8, 3.2, 8.5, 8.2, 12.5);
my @orderedIndexes = sort{
    $array[ $b ] <=> $array[ $a ]
} 0 .. $#array;

my $n = @array;
$array[ $_ ] *= @array / $n-- for @orderedIndexes;

print "@array";
__END__
c:\test>junk68
15 9.6 9.6 10.2 12.3 12.5
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