You have a 5 question multiple choice test. each question has 4 choices. you don't know any of the answers. what is the experimental probability that you will guess exactly three out of five questions correctly

You can calculate the theoretical probability, but to find out the experimental probability, you need to actually do it. Take the test a bunch of times. Find out how may times you got exactly 3 correct answers, and divide by the number of times you took the test.