Experiment Design and Identifying Bias Practice Test

Krystal owns a boutique clothing store, and wants to learn more about her customers. She sends out a survey to the 35 customers who spent the most money in her store last month. Is this sample of customers likely to be biased?

Medical data shows it can take more than 4 months to recover from knee replacement surgery. A team of researchers is conducting an experiment to see if a new rehabilitation program can help reduce this time. The researchers ask 80 randomly chosen knee replacement patients to use the new program. They then note the recovery time for each patient.

Is this a statistically well designed experiment?