Question

Past records from a large supermarket show that 20% of people who buy chocolate bars buy the family size bars. On one particular day a random sample of 30 people was taken from those that had bought chocolate bars and 2 of them were found to have bought a family size bar.
1) test at the 5 % significance level, whether or not the proportion of people who bought a family size bar of chocolate that day had decreased. State your hypothesis clearly.