Can you Help me With Math Problems?

The second one you have to do on your own, you must see and draw I'm sorry. But the first is easy, the answer is 1/20th of a chance because you have 20 key's one lock 1 work's. Ans he 1 out of those 20 chance of it working his first time. He messed up because he counted it as if he had 2 key's and it was a 50% chance his one key he grabbed was going to work or not witch is .50. But it's more like saying it ether doesn't work 19 times or does. But just it ether or doesn't. Hope I helped.