Common mistakes
The second and third radicals are the same letter. They merge: رَدَّ: and come apart again before a consonant ending: رَدَدْتُ.
اِسْتَعْدَدَ → اِسْتَعَدَّ Past: heاِسْتَعْدَدَتْ → اِسْتَعَدَّتْ Past: sheاِسْتَعْدَدُوا → اِسْتَعَدُّوا Past: they (m.)يَسْتَعْدِدُ → يَسْتَعِدُّ Present: he