zweistellige

Zweistellige is the German adjective used to describe numbers that consist of two digits, typically in the decimal system. It applies to numbers from 10 to 99. In practice, the term appears in phrases such as zweistellige Zahl (a two-digit number) and zweistellige Zahlen (two-digit numbers). The concept is commonly used in mathematics, education, and data categorization.

Origin and form: The word combines zwei ("two") with stelle, derived from Stellen meaning positions in a number’s digit representation. The base form is zweistellig; "zweistellige" is the attributive ending used before feminine nouns, such as Zahl (singular) or Zahlen (plural), in standard German grammar. For example, "eine zweistellige Zahl" and "zweistellige Zahlen" are correct usages.

Numerical properties: Two-digit numbers have a tens digit in the range 1–9 and a units digit in 0–9. There are 90 two-digit numbers in total, from 10 up to 99. They can be represented as 10a + b with a ∈ {1,...,9} and b ∈ {0,...,9}. In educational contexts, two-digit numbers are often used to illustrate place value, addition and subtraction, and basic probability.

Related terms and usage: Related concepts include einstellige (one-digit) and dreistellige (three-digit) numbers. In programming and data formatting, two-digit fields are common and may require zero-padding to maintain fixed width (for example 01, 02, up to 99).