A science teacher presented a balloon to his class, and posed the question, "If I keep this balloon in the freezer overnight, what will occur?" He followed up with, "How certain are you of your answer?" The teacher recorded his students' responses. Certain Uncertain Shrink 5 7 11 15 Stay the same Expand 4 4 What is the probability that a randomly selected student believes the balloon will expand or was certain? Simplify any fractions