And if it is God's purpose that the coin come up heads, what do you think the chances are that it will come up tails?
And in such a case, did God arrange it or merely allow it to happen?
Did God purpose and arrange for your salvation? Or did he merely allow it to happen?
I believe (correct me if I am wrong) your confusion on this issue is in part due to an incorrect notion of time.
For man, we are on a linear scale. Time moves forward with no possibility of going back (unless you like SF books). God is not that way. God sees all time as NOW! Thus, the Flood, the Incarnation, and World War 2 are all seen in the sweep of one eternal glance by God.
Perhaps this analogy will help (from Fr. Reginald Garrigou-Lagrange)
Imagine a huge mountain. Picture millions of people standing around this mountain, in single file, entirely circling this mountain. Each person represents one year of time in ascending order. Now. God has a bird's eye view from the top of the mountain. He sees all time (the people) simultaneously. Thus, what "year one - Adam" is doing is happening simultaneously as "year 4000 - the Incarnation" and "year 6000 - today".
What does this mean? God doesn't make a plan like we do. He doesn't start from "human day one" and then move things along. Since His view of time is different then ours, He "plans" in the NOW. Thus, our free-will decisions are PART of God's Plan, since it all occurs to Him right now.
It is a mystery. But I think it helps to explain a little the mystery of God's foreknowledge and God's ordination. That God knows the coin flip will be tails is taken into account. His plan takes our input and actions into account.
Regards