A call centre claims that the amount of time a worker spends on each phone call can be modelled by a normal distribution with a mean of 8 minutes and a standard deviation of 2 minutes.
Using this model, find the probability that the time the worker spends on a randomly selected phone call is more than 11 minutes.
The call centre manager thinks that the mean time for each phone call is more than 8 minutes. The manager takes a random sample of 20 phone calls and finds that the average time is 8.8 minutes. Test the manager's belief at the 5% significance level. You should state your hypotheses clearly.
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.