Rule 1: 1. Fractions from a third to a tenth
From three to ten the fraction is formed on the pattern فُعْلٌ or فُعُلٌ from the root of the number: ثُلُثٌ (or ثُلْثٌ) a third, رُبْعٌ a quarter, up to عُشْرٌ a tenth. The plural is أَفْعَالٌ: أَثْلَاثٌ، أَرْبَاعٌ. A half is نِصْفٌ (pl. أَنْصَافٌ). The fraction is a noun: it stands in construct before the whole (ثُلُثُ الْمَالِ), takes the dual for 'two' (ثُلُثَانِ, ثُلُثَا الْمَالِ), and after numbers 3–10 the plural (ثَلَاثَةُ أَرْبَاعٍ three quarters).
ثُلُثُ الْبَاعَةِ مِنَ الْقُرَى الْمُجَاوِرَةِ.
thuluthu l-bāʿati mina l-qurā l-mujāwirati.
A third of the sellers are from the neighbouring villages.
بَاعَ نِصْفَ بِضَاعَتِهِ قَبْلَ الظُّهْرِ.
bāʿa niṣfa biḍāʿatihi qabla ẓ-ẓuhri.
He sold half his goods before noon.
ثُلُثَا الزَّبَائِنِ مِنَ النِّسَاءِ.
thuluthā z-zabāʾini mina n-nisāʾi.
Two thirds of the customers are women.
Dual in construct loses its ن.
اِنْتَظَرْتُهُ ثَلَاثَةَ أَرْبَاعِ السَّاعَةِ.
intaẓartuhu thalāthata arbāʿi s-sāʿati.
I waited for him three quarters of an hour.
اِنْخَفَضَ السِّعْرُ بِمِقْدَارِ الْعُشْرِ.
inkhafaḍa s-siʿru bi-miqdāri l-ʿushri.
The price fell by a tenth.