Students\textquotesingle~seat numbers are from $$1$$ to $$35$$. How many times does digit $$3$$ appear? (adapted from $$2002$$ Math Kangaroo Problem, Level $$3$$ - $4$, Question \#$9$) 
Overseas Competition->Knowledge Point->Number Theory Modules->Place Value and Number Bases->Applying the Principle of Place Value->Questions Involving Applying Place Value Principle
The digit $3$ appears in the ones place: $3$, $13$, $23$,  The digit $3$ appears in the tens place: $30, 31, 32, 33, 34, 35$  In total, $3 + 6 = 9$. 