A professor teaches a very small class with only 4 students. One day, when returning a test, the professor simply shuffles the tests and hands each student one of the tests at random.
(Write all answers as fractions, not decimals) What is the probability all 4 students receive the correct test?
What is the probability that no one receives the correct test?|
What is the probability that one or more students receive the correct test?

Titus works at a hotel. part of his job is to keep the complimentary pitcher of water at least half full and always with ice. when he starts his shift, the water level shows 4 gallons, or 128 cups of water. as the shift progresses, he records the level of the water every 10 minutes. after 2 hours, he uses a regression calculator to compute an equation for the decrease in water. his equation is w –0.414t + 129.549, where t is the number of minutes and w is the level of water. according to the equation, after about how many minutes would the water level be less than or equal to 64 cups?