"Un deg dau"
As a primary school child in Wales in the 1940s/50s I learned the numbers as un a ddeg, dau ddeg, tri a ddeg, pedwar a ddeg, pumpddeg, un a bumpddeg, dau a bumpddeg, dau naw, pedwar a bumpddeg, ugaen (can't spell - sori). And dau, tri, pedwar also had feminine versions, dwi, taer, pedaer (probably all spelt wrong - we were only taught to speak Welsh). Has all this changed?
How do you know when to use "un deg dau" or "ddeuddeg" or are they interchangeable
As far as I know, the "traditional" numerals such as deuddeg, pumtheg, deunaw, ugain are usually used:
- for "round" minutes of the day (20 past, 25 past, 25 to, 20 to)
- for hours of the day (1-12)
- for days of the month (1-31)
- sometimes for age, especially up to about 30 or so
- sometimes for round sums of money (e.g. £40)
Otherwise, it's usually the "modern" numerals such as un deg dau, un deg pump, un deg wyth, dau ddeg.
With the caveat that "20" on its own may be ugain even if you're otherwise using modern numerals to reduce the risk of confusion between dau ddeg (20) and deuddeg (12).