[tex]1\ \textless \ 2x\ \textless \ 27\\
Dam\:lui\:x\:valori\:pana\:cand\:2x \geq 27\\
x=1\rightarrow2x=2\ \textless \ 27\\
x=2\rightarrow2x=4\ \textless \ 27\\
\vdots\\x=13\rightarrow2x=26\ \textless \ 27\\
x=14\rightarrow2x=28\ \textgreater \ 27\\
deci\:x\in\{1,2,3,...,12,13 \}.
[/tex]
Prin urmare, multimea este formata din 13 elemente.