"How many mangoes is the total?"
Translation:Jumla maembe mangapi?
It is hard to explain but i think here as 'total' is an adjective which in swahili is 'jumla' , it is like ; total, how many mangoes? = jumla, maembe mangapi? If 'ni' would be used here it would play a role of emphasizing, but not would it be necessary otherwise.