Common mistakes
The root ends in و or ي, and the endings themselves change. Three patterns cover it: دَعَا يَدْعُو, رَمَى يَرْمِي and نَسِيَ يَنْسَى.
اِشْتَرَيَ → اِشْتَرَى Past: heاِشْتَرَيَتْ → اِشْتَرَتْ Past: sheاِشْتَرَيُوا → اِشْتَرَوْا Past: they (m.)يَشْتَرِيُ → يَشْتَرِي Present: he