A quality control manager wants to see how many defective products come off the line on average per day. They take 10 random units produced over the course of the day from each of 10 machines to test if they are defective. What type of sampling method is this?

• A. Simple random sampling
• B. Stratified sampling
• C. Cluster sampling
• D. Systematic sampling

Answer: (B)

Verified step by step guidance

1. Understand the problem: The quality control manager is dividing the production process into groups (machines) and then taking a random sample from each group. This is key to identifying the sampling method.
2. Review the definitions of the sampling methods: Simple random sampling involves selecting units randomly from the entire population. Stratified sampling involves dividing the population into strata (groups) and taking random samples from each stratum. Cluster sampling involves dividing the population into clusters and selecting entire clusters randomly. Systematic sampling involves selecting every nth unit from the population.
3. Identify the groups in the problem: Here, the machines represent the strata (groups), and the manager is taking random samples from each machine.
4. Match the method to the problem: Since the manager is dividing the population into groups (machines) and taking random samples from each group, this aligns with the definition of stratified sampling.
5. Conclude that the sampling method used in this problem is stratified sampling, as the population is divided into groups (machines) and random samples are taken from each group.