"Did you reduce the number of hours?"
Translation:Avez-vous réduit le nombre d'heures ?
"Réduire" is a 3rd group verb. The past participle is "réduit(s)" in the masculine, and "réduite(s)" in the feminine.
When knowing that this is a 3rd group verb, it's kind of obvious. The problem is how can I know which group is the right one for each verb? When it's your native language it could be automatic, but when you learn the language, how can you possibly remember the right place for more than 9000 verbs? There has to be some trick (I hope...)
1st group (70% of all verbs): the infinitive ends in -er (manger)
2nd group: the infinitive ends in -ir, and the 1st person plural ends in -issons (finir)
3rd group: all the others, with variants in the endings, especially in the past participle.
You cannot memorize them all, of course, but you can learn frequent verbs by heart and duplicate the conjugations for verbs which have the same ending, like "app||rendre, comp||rendre, p||rendre, surp||rendre" (past participle ending in -pris) and "dét||endre, ent||endre, p||endre, r||endre, t||endre, v||endre" (past participle ending in -du)
To be honest with you, it is a tough nut to crack and you will need to look them up quite often.