Given that $$M=\overline{3abcd}$$, $$N=\overline{abcd3}$$ , and $$M-N=3177$$, what is $$\overline{abcd}$$? 
Overseas Competition->Knowledge Point->Number Theory Modules->Place Value and Number Bases->Applying the Principle of Place Value
$$M-N=3177$$  $$(30000+\overline{abcd})-(10\times \overline{abcd}+3)=3177$$  $$30000-3177=9\times \overline{abcd}$$  $$\overline{abcd}=2980$$. 