Do approximate amount statements require singular or plural?
In Italian to say an approximate quantity, you would say,

about 10 = una diecINA

and that you can use this for numbers 15, 20 and then in tens up to 90

what I need to ask is, in my book

‘about 15’

is listed with a PLURAL ending

una quindicINE

but why has ‘about 10’ got a singular ending?

How therefore do I write about 20, 30, 40, 50 etc, with SINGULAR or PLURAL endings?

Hope someone may be able to help

Thanks

Kayleigh

Question

Do approximate amount statements require singular or plural?
In Italian to say an approximate quantity, you would say,

about 10 = una diecINA

and that you can use this for numbers 15, 20 and then in tens up to 90

what I need to ask is, in my book

‘about 15’

is listed with a PLURAL ending

una quindicINE 

but why has ‘about 10’ got a singular ending?

How therefore do I write about 20, 30, 40, 50 etc,  with SINGULAR or PLURAL endings?

Hope someone may be able to help

Thanks

Kayleigh

Answer

Ciao,
si dice una decina (o diecina), una quindicina, una ventina, una trentina, sempre al singolare (sempre che vengano precedute da "una"). 
Certo potresti anche dire, "due, tre, quattro decinE, etc".

Answer

Per divertimento, mi sono messo a cercare nel treccani.it e ho anche trovato:
tredicina, quattordicina e sedicina (!!). Ma, perché no "undicina"?, suona anche bene, ha ha :).

Answer

Una decina,due decine....e non dimentichiamoci della "mezza dozzina"=6 e della dozzina=12 e 2 o 3....5 dozzine

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