The “standard” Hebrew Alphabet has 22 Letters. Five of those 22 Letters can be, and often are, written differently when they occur as the last letter of a word.
This means that Hebrew has 27 Letter “Shapes” that can be used to represent numbers. With 27 Letters, Hebrew can be used to represent numbers as high as 900. (With 22 Letters, the last letter, Tau, “stops the numbering” at 400.