其它
Bill writes down all the numbers from $1$ to $60$ inclusive. How many times does he use the digit $5$? 
Overseas Competition->Knowledge Point->Number Theory Modules
In tens place: there are ten $$5$$s: $$50\sim59$$  In ones place: there are six $$5$$s: $$5, 15, 25, 35, 45, 55$ 