Answer:
To obtain a stratified sample of 30 participants, we divide the people according to their destination, ending up with four groups(Naples, Liverpool, Barcelona, Paris). Finally, we choose some members each of those groups. Adding the members choosing from all groups, we have 30 members.
Explanation:
Samples may be classified as:
Convenient: Sample drawn from a conveniently available pool.
Random: Basically, put all the options into a hat and drawn some of them.
Systematic: Every kth element is taken. For example, you want to survey something on the street, you interview every 5th person, for example.
Cluster: Divides population into groups, called clusters, and each element in the cluster is surveyed.
Stratified: Also divides the population into groups. However, then only some elements of the group are surveyed.
In this question:
A stratified sample divided all the people into groups, and then surveyes some elements(some people) of each group.
Population: 390 people in the terminal.
Groups: 4 groups. Those traveling to Naples, those traveling to Barcelona, those traveling to Paris and those traveling to Liverpool.
Stratified sample of 30:
To obtain a stratified sample of 30 participants, we divide the people according to their destination, ending up with four groups(Naples, Liverpool, Barcelona, Paris). Finally, we choose some members each of those groups. Adding the members choosing from all groups, we have 30 members.