In a hypothesis test, we use a sample to gain insight on what is likely the outcome for the population.Inyour example, that is a probability of 1 out of 20 as there were 20 people in the class.A hypothesis test might test the idea that if individuals had an extra million dollars, 20% would give that money to charity.We could then test among a sample what they would do with the money and see if 20% of the sample said give it to charity.