League-of-legends – how are LP(League Points) acquired

Okay, from my experiments, it goes:

Armor/MR reductions <--> Percentage Reductions
(They stack multiplicatively, so order is irrelevant)

Flat Reductions

This makes sense, since if flat reduction was the first thing applied, after armor, it may have failed to provide a benefit at all (since, for instance, the difference between 50 * 27% and 48 * 27% is minute at best. 50 and 27% being the base attack damage of Ezreal and the armor of Amumu, my two test characters.)

Shields act as health, and damage done to shields is likewise reduced by armor / magic resist. (Meaning shields on tanks can generally absorb more punishment than shields on squishies)

Sadly, there's no sure-fire way of resolving this situation.

You won't be able to rely on minions to take out their towers and nexus, especially if their uber status gets to the point where they can start defending their respawning inhibitors. If you get really lucky and get their nexus towers down, you could just farm minions hard enough for yours to take the nexus down a bit then try to dive the nexus. I'd consider this a Hail Mary more than anything else, though.

If you know you're going up against a team that is going to steamroll you once they get maxxed out (2+ carries), the main goal is to take advantage of the fact that they will be weaker in the early game. If you zone the carries and/or kill them enough to keep them from getting geared and leveled, your team will get powerful enough to take their nexus before they can do anything about it.

Assuming you find yourself in that unfortunate position anyway and forcing their team to split up isn't working, you absolutely have to focus the primary damage dealers down first. If they stick together and you're not killing their carries first, you'll take way more damage than you will deal out over the course of the fight and you're sure to lose.