Enuntul~este~echivalent~cu:
"Avem o carte cu 100 de pagini.
Aflati numarul cifrelor necesare pentru paginarea cartii."
.
[tex]\displaystyle\bf\\Rezolvare:\\\\De~la~1~la~9.........~n=9~numere~de~o~cifra=9~cifre\\\\De~la~10~la~99.........~n=99-10+1=90~de~numere~de~2~cifre.\\~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~90\times2=180~de~cifre\\\\100~are~3~cifre.\\\\Total:~~9+180+3=\boxed{\bf192~de~cifre}[/tex]