You're trapped in the Prison Tower of Contrivances. Fortunately, you've managed to pry open bars on the window to your cell. Unfortunately, the window is half way up the two hundred foot tall tower. Conveniently, two fifty-foot ropes are tied to two iron rings in the ceiling of your fifty-foot tall cell. The iron rings (and consequently the ropes) are about a foot apart. Your confinement has weakened your bones somewhat, so you cannot safely fall more than a few feet without risking serious injury. But your upper-body strength and climbing skills are top-notch. Armed only with a pocket knife, how much of the rope can you liberate to aid in your escape?

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A little ingenuity combined with upper-body strength will let you claim the entire hundred feet.
First, tie the two ropes together at the bottom.
Next, climb one of the ropes.
Once you're at the top, cut the other rope at the ring.
You now have a hundred feet of rope tied together.
Feed the loose end of the rope through the ring, and pull through just enough slack that it touches the floor.
Grab the ring that the rope feeds through, and cut the other end of the rope free.
You may want to drop your knife at this point and grab both ends of the rope, or the momentum of the falling rope might be enough to drag the other end through.
You now have a hundred feet of rope looped through one ring.
Holding onto both halves, slide down to safety and then pull the rope after you.