"Cúig phráta, le do thoil."
Translation:Five potatoes, please.
Nouns following numbers stay in the singular form. As well, following certain numbers, the noun is either lenited (1-6) or eclipsed (7-10) (and the same pattern with the teens and so on - lenition on 11-16; eclipse on 17-19; no change on 20; lenition 21-26; eclipse 27-29).
If you're using the desktop version, there is info in the tips and notes section for numbers. Here's a link to the page: https://www.duolingo.com/skill/ga/Numbers
There is a Russian anecdote from 70-90s almost about the same. First of all - the russian student was considered then as poor and therefore hungry. So, the story: The student came to students' diner and ordered 5 sausagies. Everybody around - wow, you became rich. The student overs his order with - ...and 10 forks.
We do love our spuds in Ireland (Spuds should be accepted as well as potatoes).
The dancer in me is annoyed that this isn't "four potatoes." "Eight potatoes" might even be acceptable, but a band would never give five.