Common mistakes
The second and third radicals are the same letter. They merge: رَدَّ: and come apart again before a consonant ending: رَدَدْتُ.
عَدَدَ → عَدَّ Past: heعَدَدَتْ → عَدَّتْ Past: sheعَدَدُوا → عَدُّوا Past: they (m.)يَعْدُدُ → يَعُدُّ Present: he