Cord-platelet count data (x 10⁹ / L) is known to exhibit a normal distribution.In 2007, 25 infants were sampled and the mean cord-platelet count was discovered to be 306, with a standard deviation of 67. We wish to determine if the mean count has changed from the original levels of mean 309 back in the year 1990. Test at the 5% significance level.

(a)Based on this scenario, state the appropriate statistical test. Explain why you came to this conclusion.

(b) State the null and alternative hypotheses for this scenario.

(c) Solve this using the critical value method.

(d) Solve this using the confidence interval method.

(e) State your conclusion for this scenario using your solutions to Questions c) and d).