The article "Why We Fall for This" (AARP Magazine, May/June 2011) described a study in which a business professor divided his class into two groups. He showed students a mug and then asked students in one of the groups how much they would pay for the mug. Students in the other group were asked how much they would sell the mug for if it belonged to them. Surprisingly, the average value assigned to the mug was quite different for the two groups! Indicate whether the study is an observational study or an experiment. Give a brief explanation for your choice.