Test yourself on the Numbers 1 to 10.
In Welsh, as with many languages, there are more to numbers than meets the eye, and some of these aspects are not intuitive to a native English speaker.
The numbers above can be used for counting in the same way as we would count in English. In other words, we can count un, dai, tri ... in welsh just like we count one, two, three ... in English.
A peculiarity of using numbers in Welsh (as above) is that when counting (things) a singular form of the noun is used. There is another way of using numbers where the number, followed by o, followed by the plural noun is used. E.g un ar ddeg o gathod 'eleven cats'.
Welsh also has alternative words for two, three and four, which are dwy, tair and pedair. These are used when describing feminine nouns. Nouns in Welsh can be either masculine or feminine.
The Welsh word for pound punt is feminine, and a commonly example illustrating using these 'different' numbers is dwy punt, tair punt, pedair punt for two, three and four pounds respectively.
Dwy, tair and pedair can only be used with feminine nouns.
The upshot of this is that to count in Welsh using this method, you need to know the gender of the noun being counted.
Cath 'cat' is a feminine noun. Mab 'son' is a masculine noun. And so you would say (or write) Dwy gath 'two cats' but Dau fab 'two sons'. The first letters have changed due to mutation which is a distinctive feature of the Welsh language, and not specific to numbers and counting.
Pump and chwech often become pum and chwe when they are used before nouns.
Mutations are ever present in Welsh. These are just some of the most commonly heard with numbers.
Feminine singular nouns mutate after un 'one'.
Un gath 'one cat'. The word cath has mutated to gath.
Ci 'dog' is a masculine word, and so 'one dog' remains as un ci with no mutation.
Both masculine and feminine singular nouns mutate after the words for two: dau gi, dwy gath.
As well as two widely used ways of using numbers in Welsh, there is another way of counting, which is through using twenties. It is not as widely used in counting (as it once was), but still important for telling the time. Looking out for this helps to remember some time related expressions.
See also the numbers 10 to 20 and the numbers 30 to 1000.
Once you are confident with numbers, it's easy to get started with telling the time in Welsh.