always wa at test 11,why?

I can't figure out what the hint about!

Why “If the order of tests is “YES-NO-NO”, then Valentine's solution won't pass the second test only; if the order is “NO-YES-NO”, then it will pass none of the tests; if the order is “NO-NO-YES”, the solution won't pass the first and the third tests.”

Can you give me more detailed explanation？

This is test #11:
5000 12500
Who have answer?

Edited by author 06.09.2013 20:53

The answer for that is 2500.50