Any native Hebrew speaker will tell you that the most confusing thing about Hebrew grammar is NUMBERS. This is true. Often you will hear native Hebrew speakers stop in the middle of a sentence because something about the number mentioned “doesn’t sound right”.
Where does this confusion come from?
There are two main reasons:
The first reason is that Hebrew numbers don’t follow the standard predictable pattern of Hebrew words.
While most (but not all) nouns that end with the vowel ‘a’ are feminine nouns, numbers that end with the vowel ‘a’ sound are masculine.
For example: SHLOSHA BATIM (“three houses”, masculine) but SHALOSH GVA’OT (“three hills”, feminine).
The second reason has is related to the nouns themselves. Many nouns have an irregular plural form. Irregular nouns might seem and sound masculine but in reality they are actually feminine or vice versa.
For example: SHLOSHA AVOT (“three fathers, masculine), but SHALOSH NASHEEM (“three women”, feminine).
Non-native Hebrew speakers learning the language find that their main obstacle is prepositions. It is hard to figure out how to pair the verb with the correct preposition, if at all. For example, in Hebrew, people are “angry about someone” (and not “angry at someone”, as in English), they are “telling to someone”, and “going in a bus”. The only way to figure out the right preposition is to look it up, or to ask a teacher.