There are $$24$$ four-digit numbers which is formed using each of the digits $$3$$, $$4$$, $$5$$ and $$6$$ once only. When all of these $$24$$ four-digit numbers are put in order from smallest to largest, which one is in the seventh position? 
Overseas Competition->Knowledge Point->Counting Modules->Questions Involving Enumeration->Enumeration
$3456, 3465, 3546, 3564, 3546, 3564$  $\underline{4356}, 4365, 4536, 4563, 4635, 4653$  $5346, 5364, 5436, 5463, 5634, 5643$  $6345, 6354, 6435, 6453, 6534, 6543$ 