Is gyfrifol related to cyfrifiadur?
Perhaps via something like "accountable" vs. "counter"?
Exactly, some alternative meanings are computable, accountable
See http://welsh-dictionary.ac.uk/gpc/gpc.html for more
why is it gyfrifol here, but gyfrifiol elsewhere?
Where have you seen "Cyfrifiol", "Cyfrifol" is the only one I've come across as a fluent Welsh speaker.
on one of the duolingo sentences. must be an error or i misremembered...