Numbers in Arabic are quite complicated; there are different rules for the numbers. Numbers are declined according to gender. Getting the grip on numbers in order to make practical use of them (few Arabs used numbers correctly), is however reasonably easy.

From 21 to 99 you count like this: (example) 24: Four wa-forty from 12 to 19 you count like this (example) 15: Five Ten. The number 11 is slightly diverging.