The Math::Pari module can evaluate mathematical expressions with a more restricted syntax than perl's -- but watch out for "system()". Here's an example.
use strict;
use Math::Pari qw(PARI);
my $question="67.35 >= 50 && 67.35 < 80";
# Pari doesn't like white space in expressions.
$question =~ s/\s+//g;
my $out = PARI $question;
print $out,"\n";