You may use existing solutions, like Bit::Vector:

use Bit::Vector;

my @probs =(0,0.1,0.53,0.51,0.59,0.67,0.2,0.04,0.05,0.56,0.89,0.75);

my $v = Bit::Vector->new(int @probs);
$v->Index_List_Store(grep { $probs[$_] > .5 } 0..$#probs);

for (my ($start, $min, $max) = 0; $start < $v->Size(); $start = $max +
+ 2) {
    last unless ($min, $max) = $v->Interval_Scan_inc($start);
    print "$min $max\n";
}
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or even use $v->to_Enum instead of above for loop and receive

2-5,9-11
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As a marginal note, you use indexes out of bounds of the array (in $probs[$_+1], when $_=$#probs), which is an error-prone practice.