I thought I would experiment and put in chwe which I believe to be a shortened form but it was mark wrong this despite the fact that the shortened form is used in some of the multiple choice questions as far as i remember.
If you go through the course notes, you will see the explanation.
The numbers pump, chwech, cant all drop their last letter when used directly in front of nouns:
- pum cath, chwe arth, can buwch - five cats, six bears, a hundred cows.
We recommend that you go through the notes for each new section before you start it.
I have previously checked the notes. As they don't make a lot of sense, I don't bother. I have since gotten a Welsh grammar book at the library. It helps. It also points out there are added complications for Welsh learners who are native English speakers and don't have a lot of experience with other languages. It would be very helpful to have information provided with that in mind.