It has to do with the last root letter, i.e., the و.
You use the dual form of a special word.
In Arabic, there is a special way to express the English word both.
The Arabic word hundred is written مِائَة – but pronounced like مِئَة.
How is it possible to have a كَسْرة before an Aleph? This is actually impossible in Arabic. Well, let’s see…
A big one.
The early works on grammar as well as the first dictionaries were very much based on the spoken Arabic of Bedouins. The grammarians regarded the Bedouin as the true speaker of Arabic.
Yes, this is possible.
Such constructions with وَ are often difficult to translate as we need different words in English.