Telephone number are often stated in groups of two, if it's uneven then the first digit is stated by itself and then the groups. (this applies to home addresses and email addresses)
87
New cards
street addresses
For street addresses the building number is given after the name of the street
88
New cards
uno masculine/feminine rules
Uno becomes un before a masculine noun (un libro, veintiún libros)
89
New cards
Uno becomes una before a feminine noun (una página, veintiuna páginas)