Here is a list of fractions.
612122591815302142 \frac{6}{12} \quad \frac{12}{25} \quad \frac{9}{18} \quad \frac{15}{30} \quad \frac{21}{42} 126251218930154221One of these fractions is not equivalent to 12\displaystyle \frac{1}{2}21.
Write down this fraction.