G'day rkd257,

Welcome to the Monastery.

"... thought I would end up with 5 and 7 ... ## $cf = 7/12 ..."

So, I think you should have been expecting 7 and 12. If not, please explain why 5 and 7?

Anyway, I think you want bigrat; not Math::BigRat and bignum. (All three are core modules.)

$ perl -e '
    use bigrat;

    my $cf = 1 - 1/6 - 1/4;
    my $n = $cf->numerator();
    my $d = $cf->denominator();

    print "$cf\n";
    print "  $n\n";
    print " $d\n";
'
7/12
  7
 12
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