To find out if customers are happy with the store hours, the Independent Grocer randomly surveyed 500 customers who bought groceries for one week.
Is this sample biased or reliable? Justify your answer.
I don't really understand what you mean by "buy groceries for one week"
If it means buy one weeks worth of groceries, it would be reliable as the customers could have been first time or long term so there is no telling if there is any bias.
If it menas buy groceries every day for a week, then it would be biased as the customers generally would not come back every day for a week if they weren't happy with the store hours.