"It is five minutes to five."
Translation:Mae hi'n bum munud i bump.
I have read that pump and chwech (five, six) usually turn into pum, chwe respectively when they stand in front of a noun.
The first one is before the noun munud, the second stands alone, which would explain the different ending.
Someone else made a similar comment in another conversation. The change in the p at the start of the word is a soft mutation, though.
With the first 5, the soft mutation changes pump to bump. Then the end of bump is dropped to form bum because it's before a noun (bum munud).
The last 5 only has the soft mutation (pump to bump) because it doesn't come before a noun.
What is the reason for changing pump to bump, and changing the form of other numbers? When do the numbers keep their normal form, and when are they different? Will it just become second nature with practice?