A logistics company claims that the average delivery time for local parcels is 12 hours. A manager suspects that recent changes in the sorting process have altered this mean delivery time. A random sample of 10 parcels is monitored, and their delivery times in hours are recorded as follows:
11.5,12.8,12.2,11.9,13.1,12.4,11.7,12.6,13.3,12.5 11.5, \quad 12.8, \quad 12.2, \quad 11.9, \quad 13.1, \quad 12.4, \quad 11.7, \quad 12.6, \quad 13.3, \quad 12.5 11.5,12.8,12.2,11.9,13.1,12.4,11.7,12.6,13.3,12.5Carry out a hypothesis test at the 5% significance level to investigate whether the mean delivery time has changed. You may assume that delivery times are normally distributed with a standard deviation of 0.6 hours.
316 exam-style questions on OCR A Level Maths 2.5 Statistical Hypothesis Testing, covering 2.5.1 The language of hypothesis testing, 2.5.2 Hypothesis test for a binomial proportion, 2.5.3 Inference and significance level, 2.5.4 Sample mean as a random variable (A-level only), 2.5.5 Hypothesis test for the mean of a normal distribution (A-level only), 2.5.6 Pearson's product-moment correlation coefficient, and 2.5.7 Hypothesis test using Pearson's coefficient (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.