The answer is 1/20. This is probability. <u><em>probability is the chance of you picking a certain thing</em></u>. for example: You have 3 blue marbles, 6 red marbles, and 4 purple marbles. the probability of pick a blue marble is 3/13. A red would be 6/13, and a purple would be 4/13.
So what this is asking is what are the chances that something will happen over something will not happen. the said that "the probability that an event will not happen is P(E') = 19/20. if you are having a lot of trouble with this, try removing the events with something like marbles (Something you have done before) this tends to make it a little easier to read.
