Question

The city wants to know if buying a giant water fall would be cost effective. They want to get an idea of how many would pay to use the slide. Which sample would give the city the most useful results?

A. 25 people of all ages
B. 100 people of all ages
C. 30 people at city park
D. 100 people at city park

Answer 1

100 people of all ages

Answer 2

100 people of all ages. If they pick any number of people at the city park, that's considered a bias, because what if the typical city park goers are in their 20s-30s? what if they're made up of ONLY dog owners? these are irrelevant details that shadow away from the true, useful, unbiased results.

Secondly, if they choose a smaller amount of people, they'll get a smaller number of responses, which could lead their study astray.