Questions & Answers about Mój syn ma dwadzieścia punktów.
Why does the word for points end in -ów here?
This is the core rule for numbers in Polish! Numbers 5 and above require the noun that follows them to be in the Genitive plural case. So instead of using the regular plural punkty, we use the Genitive plural punktów (which translates literally to: twenty of points).
How do I know to use the -ów ending for punkt in the Genitive plural?
Punkt is a regular masculine noun ending in a consonant. The vast majority of masculine nouns that end in a hard consonant take the -ów ending when changing to the Genitive plural.
What case is the number dwadzieścia in?
It is in the Accusative case, because the entire phrase dwadzieścia punktów is the direct object of the verb ma (to have). For numerals 5 and above, the Accusative form looks exactly the same as the basic Nominative form you memorize.
Why doesn't the possessive pronoun mój change to match the Genitive plural case?
The possessive pronoun mój describes syn (son), which is the subject doing the action. Therefore, mój syn stays in the basic Nominative case, completely unaffected by the grammar rules happening in the second half of the sentence.