A school principal wants to find out what the students think about the teaching quality in the school. Which of these samples is unbiased?
An animal rescue center wants to find out if people in its town think more money should be spent on animal welfare. They plan to ask a random sample of their visitors and volunteers to fill in a questionnaire. Why would their sample not be representative of the town’s population?
A teacher wanted the children in her class to have a random sample of coins for a lesson. She put nickels, quarters, and dimes into a bag, and the bag was passed around the class for each child to select a coin without looking in the bag. Why is this unlikely to produce a random sample of coins?