A school principal needs to pick a student at random to appear in a commercial. In order to be fair, she decides to put the names of students on pieces of paper and pick one at random from a hat. She puts the names of 100 5th grade, 100 6th grade, 100 7th grade, and 100 8th grade students in the hat. a) Create a probability model showing the theoretical probabilities of a student from each grade being chosen:
b) Does this show a uniform probability model? Explain.​