Yaakov (Jacob) had 12 sons and one daughter. According to one opinion each of his children was born with a twin sister with the exception of Yosef (Joseph) and Dinah [Pirkei D’Rebbi Eliezer Ch. 36]. So, in total, how many daughters did Yaakov have?
12 son – Yosef = 11 sons who each had a twin sister = 11 twin girls
11 twin girls + Dina = 12 daughters