"Hizi ni simu mpya"

Translation: These are new phones

[vitoreiji]

Why is it mpya? Shouldn't the adjective take a class 10 prefix?

[likes2hike]

You're right that the adjective takes a class 10 prefix. For plural N-class (class 10) nouns such as "simu," this prefix is "n-." However, because the adjective stem in this case begins with a "p" sound, the prefix changes to "m-," hence "mpya." More cases where the prefix for this class changes at: https://en.wiktionary.org/wiki/Appendix:Swahili_noun_classes#N_class

[AGreatUserName]

Just to add to this ... normally, there is no prefix in class 9/10 before "p" or other voiceless sounds, but because "pya" would only be one syllable, the N- prefix must be kept so that there can be a stressed second-last syllable, and, of course, it is assimilated to the "p".

[BlerinaPro]

Why didn't my answer: these are the new phones - get accepted?! Why is it wrong to include "the" ?!