"One year is twelve months"

Translation: Mwaka mmoja ni miezi kumi na mbili

[Deborah712044]

In another exercise it says miwili and mbili is wrong! This one is the opposite!

[Mr_Kasanje_146]

Shouldn't it be "miezi kumi na miwili"?

[machieng]

I'm always forgetful of which numbers need noun class prefixes, but I believe you're right

[AGreatUserName]

According to the Bakita rules it's all numbers ending in -moja, mbili/-wili, -tatu, -nne, -tano ... and -nane. A lot of people only do it for these numbers below ten though.

[dsimonds]

The old grammar books teach you "viti kumi na viwili". The first time a native speaker heard me say that he laughed his head off. I started saying "viti kumi na mbili" :)

[Ernst557459]

Well, it seems that both are used. A Google search for "kumi na wawili" yields 320,000 hits, kumi na miwili 60,000, kumi na viwili 14,000, whereas kumi na mbili gives just over 1 million hits. But the latter would include all the N/N class plurals. So, maybe your native should keep a level head on not detach it to readily :)