Question

1. An automatic welder is used to join a large number of tubes in a heat exchanger assembly. Each weld is inspected, and most of them are satisfactory. However, some need repair by a re-machining and re-welding process. In a sample of 65 qualification welds, eight were found to require the repair process.

1. Perform the appropriate hypothesis test to determine whether there is evidence that the repair probability differs from 10%.

2. A very approximate 100·(1 – a)% confidence interval for a binomial proportion, based on a sample of n items, is given by:

Suppose you wanted to estimate the probability of a weld requiring repair to within ±0.05, with 95% confidence. What sample size would you recommend using?

Answer 1