Common mistakes
The second and third radicals are the same letter. They merge: رَدَّ: and come apart again before a consonant ending: رَدَدْتُ.
أَعْدَدَ → أَعَدَّ Past: heأَعْدَدَتْ → أَعَدَّتْ Past: sheأَعْدَدُوا → أَعَدُّوا Past: they (m.)يُعْدِدُ → يُعِدُّ Present: he