I had a 5 in logistics =)
What makes this 5 especially valuable is that I managed to get it, because these types of problems are incredibly difficult. Otherwise, sometimes you come to an exam for a subject, and at the beginning they ask: who are you?, and at the end they give you a 5, which is uninteresting.

Added 2 minutes ago

K.O. suggests that they are solved by building a mathematical model!

I don't know how it's solved scientifically; we drew some kind of tables in class and filled in numbers, and it somehow solved itself =)

Added 1 minute ago
And who is K.O.?
Will you introduce me?
It's more than certain that it's Olga.

Added 8 hours 22 minutes ago
Hmm, I've been thinking...
Maybe it's some kind of Katerina Olegovna! and not Olga at all...