A biased sample is ond where all individuals were not given equal likelihood of being selected.
Number 1;
Picking students from the cafeteria would lead to sampling bias because not every student from the school eats from the cafeteria. Those she selected can not be used to account for the whole school. Those that use the cafeteria are only a representation of the whole school and not the entire school.
For number 3:
Paul is interested in finding the mean number of cloth shoppers In a mall and is only collecting data from one clothing store without considering other stores in the mall.
