Free Will

Christians commonly claim that god granted us free will, and does not interfere with the daily lives of people.
We make our own choices.
That's why there is evil and suffering in the world.

So why pray for things ?
Wouldn't the answering of a prayer contradict the concept of non-intervention ?
Wouldn't intervention contradict the concept of free will ?
(even if not for the one praying, certainly for others affected)

Also:
If god is omniscient, he must know the future.
If god knows the future, he must know what we will do.
If god knows what we will do, it must be in some way pre-determined.
If our actions are pre-determined, we do not have free will.