An Internet service provider sampled 540 customers and found that 75 of them experienced an interruption in high-speed service during the previous month.

a. Find a point estimate for the population proportion of all customers who experienced an interruption.

b. Construct a 90% confidence interval for the proportion of all customers who experienced an interruption.

c. The company’s quality control manager claims that no more than 10% of its customers experienced an interruption during the previous month. Does the confidence interval contradict this claim? Explain.