Answer Happy

The Minitab output below summarises the statistics of the deflection temperature under load (in°C) for two different types of plastic pipe. Descriptive Statistics: Pipe 1, Pipe 2 Variable N Mean Variance Pipe 1 15 91.33 Pipe 2 12 88.56 33.90 31.23 Assume the population distributions of the deflection temperature under load to be normally distributed.

(a) Construct a 98% confidence interval for the standard deviation of pipe 2's deflection temperature under load and interpret the interval. (b) Find the 95% confidence interval for the ratio of variances of the deflection temperature under load for all the two types of pipe. Explain what can be concluded from this interval? (c) From the result obtained in (b), construct a 95% confidence interval for the difference in the mean deflection temperature under load for all the two types of pipe. Based on this interval, is the deflection temperature under load for pipe 1 higher than pipe 2 on average? Justify your answer.