# review and reflections

1. Waiting times for customers in an airline reservation system are (in seconds) 953, 955, 948, 951, 957, 949, 954, 950, 959.

a. Calculate the sample average.

b. Calculate the sample standard deviation.

2. Monthly sales for tissues in the northwest region are (in thousands) 50.001, 50.002, 49.998, 50.006, 50.005, 49.996, 50.003, 50.004.

a. Calculate the sample average.

b. Calculate the sample standard deviation.

3. Draw the type-B OC curve for the single sampling plan.

4. An electronic component in a dental x-ray system has an exponential time to failure distribution with . What are the mean and variance of the time to failure? What is the reliability at 30,000 hours?

5. A synthetic fiber is stressed by repeatedly applying a particular load. Suppose that the number of cycles to failure has an exponential distribution with mean 3,000 cycles. What is the probability that the fiber will break at 1,500 cycles? What is the probability that the fiber will break at 2,500 cycles?