iPod reliability. MacInTouch reported that several versions of the iPod reported failure rates of 20% or more. From a customer survey, the color iPod, first released in 2004, showed 64 failures out of 517. Is there any evidence that the failure rate for this model may be lower than the 20% rate of previous models?
a) Find the z-score of the observed proportion.
b) Compare the z-score to the critical value for a 0.1% significance level using a one-sided alternative.
c) Explain your conclusion.