That's not a regexp, so the re pragma won't help here. However, the built-in eval function will:

#!C:/perl/bin/perl.exe

use warnings;
use strict;

my $question = "67.35 >= 50 && 67.35 < 80";
my $ans = eval $question;
die("Compile error: $@\n") if $@;
print("ans = ", ($ans ? 'true' : 'false'), "\n");
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Beware including user-supplied data in an eval. Users are sometimes malicious or supply unexpected data.